Question for anyone familiar with manual focus lenses ...
Discussion
Being a 35mm SLR user - indeed vintage 35mm at that - I have manual focus lenses.
Recently I obtained a manufacturer's 2x Extender to play with and, added to my 75-200 zoom, it produced pretty good results as a 150-400. However I have seen a few shots that were 'soft' and I decided that must be down to me and the focusing handling near the infinity position when the poor old lens seem to slip passed best focus and get a touch blurred.
So I tried some tests using neighbours TV aerials as targets - and got some very odd results. Like the target was out of focus but other objects - walls and rooftiles mostly, some distance beyond it were in excellent focus. Someone suggested camera shake but I think not in all the test examples.
With the 2x extender it is a little tricky to make any use of the split prism focusing facility, but sometimes, with care, it becomes usable.
Anyway, today I was wondering about this probelm and thought that perhaps I need to look at dioptre adjustment lenses. But as far as I know my prescription is within the inclusive adjustment of the viewfinder and I don't experience any problem focusing on the focusing screen.
So I spent a little time experimenting late last afternoon and was very surprised by the results.
Although my prescription is identical for both eyes if I set the focus on the lens using my dominant left eye checking the focus with my right eye suggested a small amount of focus adjustment would be required.
If I add my spectacles into the mix the preception of what was and was not in focus changed once again - accoring to the marklings on the lens by about 5 meters or so on a focus distance of about 15 to 20 meters - quite a bit.
Now this puzzles me as my understanding is that one is simply focusing on the screen, percieved to be an object about 1 meter away through the viewfinder, at which distance I don't require any correction.
In turn that means the split prism should be providing visual indication suited to the 1 meter distance.
So I am slightly baffled.
Other than blowing a few grand and changing all my kit to Digital and AF, has anyone got any suggestions?
I will now be running another test or two but any insights about what to seek out would be gratefully accepted.
Recently I obtained a manufacturer's 2x Extender to play with and, added to my 75-200 zoom, it produced pretty good results as a 150-400. However I have seen a few shots that were 'soft' and I decided that must be down to me and the focusing handling near the infinity position when the poor old lens seem to slip passed best focus and get a touch blurred.
So I tried some tests using neighbours TV aerials as targets - and got some very odd results. Like the target was out of focus but other objects - walls and rooftiles mostly, some distance beyond it were in excellent focus. Someone suggested camera shake but I think not in all the test examples.
With the 2x extender it is a little tricky to make any use of the split prism focusing facility, but sometimes, with care, it becomes usable.
Anyway, today I was wondering about this probelm and thought that perhaps I need to look at dioptre adjustment lenses. But as far as I know my prescription is within the inclusive adjustment of the viewfinder and I don't experience any problem focusing on the focusing screen.
So I spent a little time experimenting late last afternoon and was very surprised by the results.
Although my prescription is identical for both eyes if I set the focus on the lens using my dominant left eye checking the focus with my right eye suggested a small amount of focus adjustment would be required.
If I add my spectacles into the mix the preception of what was and was not in focus changed once again - accoring to the marklings on the lens by about 5 meters or so on a focus distance of about 15 to 20 meters - quite a bit.
Now this puzzles me as my understanding is that one is simply focusing on the screen, percieved to be an object about 1 meter away through the viewfinder, at which distance I don't require any correction.
In turn that means the split prism should be providing visual indication suited to the 1 meter distance.
So I am slightly baffled.
Other than blowing a few grand and changing all my kit to Digital and AF, has anyone got any suggestions?
I will now be running another test or two but any insights about what to seek out would be gratefully accepted.
I can't (it's too early and not enough caffeine) think through the physics, but as I commented recently, your eyesight does need to be up to par if you want to ensure accurate focus onto a ground glass screen, fresnel screen or split...
...thingy
(again without caffeine, so I can't think of the technical worm...)
My old man used to have trouble getting sharp shots, while I could with the same and similar kit. I would wear my glasses, he wouldn't! (Both short-sighted, btw.)
The fact that you are getting something in focus proves it is possible to get focus with that lens. So either the distance from lens to screen differs from lens to film plane (possible!), or your eyesight is such that you are perceptably "mis-placing" the focus point. The effect is just more obvious because your focus is more critical with longer focal length....
Edited to say "prism" - yeah, I know I just read that. Gone to put the kettle on, back in five....
>> Edited by beano500 on Friday 30th September 09:29
...thingy
(again without caffeine, so I can't think of the technical worm...)
My old man used to have trouble getting sharp shots, while I could with the same and similar kit. I would wear my glasses, he wouldn't! (Both short-sighted, btw.)
The fact that you are getting something in focus proves it is possible to get focus with that lens. So either the distance from lens to screen differs from lens to film plane (possible!), or your eyesight is such that you are perceptably "mis-placing" the focus point. The effect is just more obvious because your focus is more critical with longer focal length....
Edited to say "prism" - yeah, I know I just read that. Gone to put the kettle on, back in five....
>> Edited by beano500 on Friday 30th September 09:29
The question is are you getting OK results without the converter?
My Father in law had big problems with these, and stopped using them in the end - the problem comes with manufacturing tolerances and the ability to focus to infinity...
If the converter is very slightly too long, you will never able to focus crisply at infinity.
My gut feeling is this is the problem you've got rather than anything wrong with the lens / camera / your eyesight...
Chris
My Father in law had big problems with these, and stopped using them in the end - the problem comes with manufacturing tolerances and the ability to focus to infinity...
If the converter is very slightly too long, you will never able to focus crisply at infinity.
My gut feeling is this is the problem you've got rather than anything wrong with the lens / camera / your eyesight...
Chris
beano500 said:
The fact that you are getting something in focus proves it is possible to get focus with that lens.... you are perceptably "mis-placing" the focus point. The effect is just more obvious because your focus is more critical with longer focal length...
That's my guess too. Focus on long lenses is critical, especially at large apertures. You'll have to be more careful, and/or use a smaller aperture.
How good are the old lenses? I tried some of my older lenses on my DSLR when I got it and whilst they seemed fine on the film one, on the DSLR they were pretty soft (with AF).
Reason being they were actually relatively cheap lenses and due to the small sensor size on the DSLR, only the middle portion of the lens glass was used (magnifying any lack of quality). You then view the result effectively zoomed in a lot on your PC to further exaggerate the effect. Try printing a shot out at 6x4 from a full frame and see if it's still noticeably soft.
The newer digital lenses are optimised around the centre of the glass (to keep cost down) and therefore will be sharper for the same cost - but you can't then stick them back on a film body.
Just my thoughts
Reason being they were actually relatively cheap lenses and due to the small sensor size on the DSLR, only the middle portion of the lens glass was used (magnifying any lack of quality). You then view the result effectively zoomed in a lot on your PC to further exaggerate the effect. Try printing a shot out at 6x4 from a full frame and see if it's still noticeably soft.
The newer digital lenses are optimised around the centre of the glass (to keep cost down) and therefore will be sharper for the same cost - but you can't then stick them back on a film body.
Just my thoughts
Do you get the same problem with the lens without the adapter or with other lenses? I am just trying to see if there is a way of eliminating the variables to see where the problem lies. Might it also be worth checking whether your current perscription is still appropriate.
Strangely my Father used to use three sets of glasses; reading, distance and photography. The photography set were a set generally about one perscription old that he swore got him better results. (However, he also reckoned he could hear better with his glasses on so may not be a wholly reliable source)
Strangely my Father used to use three sets of glasses; reading, distance and photography. The photography set were a set generally about one perscription old that he swore got him better results. (However, he also reckoned he could hear better with his glasses on so may not be a wholly reliable source
)chris.mapey said:
The question is are you getting OK results without the converter?
Good question, well presented, deserves and answer.
I don't know - I wish film captured the same information about the shot that digital does!
The problem really is that the only way to test that sort of thing is to take still subject shots at a consistent distance.
I did this when I got the extender, shooting some flowers in a pot on the patio at a distance of about 20ft approx. I was impressed with the results when combined with the manufacturer lens. They were less good with a third party lens colour edging showing (technical term does not come to mind instantly!) quite markedly at the 400mm zoom level - but then I was not totally surprised at that!
Obviously one expects a shallow depth of field with virtually no latitude before the focus distance.
Anyway, the closer test point in my more recent tests seems to be about 70 ft away as best I can estimate - if it stops raining and I can find a long enough measure I may check that more accurately.
Without taking any shots I have been focusing on the thin vertical aerial support pole. Tried a few lenses - 2 zooms and a 50mm prime - and once a focus is set I can switch eyes and include/exclude specs and see little or no difference to the split prism alignment.
Add the extender (checked with the manufacturer's zoom and prime) and the focus seems to be shifted quite markedly. With the zoom, I could get noticably different results by changing the eye position relative to the viewfinder.
With the extender fitted to the thirdparty zoom lens (which is faster than the manufacturer lens so the split prism is still usable even on a dull day like today), eye to eye there is no discernable difference throught the split prism (as I would expect). Include the specs and there is a very slight difference but nothing like as much as with the other lenses.
So, when wearing specs the focus seems to be set further away. Just a tad on the focus control but that could be 10 or 20 feet at that distance.
Oddly I doubt that I would have been wearing specs when taking the earlier shots so the results as I see them (no pun intended) are baffling.
I have now checked the effect with all three camera bodies in my possesion and it is pretty much the same on all of them though one, the one I originally used, seems to be more evidently prone to the shift than the others. Interestingly I also discovered what a superb screen the old Canon F1n has in terms of brightness of image. The split prism is, to all intents and purposes, unusable on my A1 with the zoom/extender combination and almost as bad on the AE1. But the F1 is just like looking through a fast prime. I had not expected that.
Hmm, maybe I should buy another F1 and dump the A1.
I think I see further testing ahead. So far I can tell there is a difference and so a need to adjust for that - but I don't have the information to decide which, if either, of specs included or specs excluded gives the correct focus.
I may need to run a few films ...
>> Edited by LongQ on Friday 30th September 11:54
LongQ said:
With the zoom, I could get noticably different results by changing the eye position relative to the viewfinder.
That sounds like a recipe for duff focusing if ever there was one, and might explain why you are getting such variable results. An image on a ground glass screen should be sharp regardless of eye position, no?
I would hazard a guess that the extra-long telephoto is putting to much of a demand on the camera's focusing aids and/or your eyes. If you want to use such focal lengths reliably, it might be time to move to an AF camera. Then you can let the camera take the strain and you can concentrate on other things like composition. AF also allows you to work much faster, if that's important.
simpo two said:
An image on a ground glass screen should be sharp regardless of eye position, no?
...operative part being "should be". Don't think it will be in the real world.
It's a real (as opposed to "virtual" ) image, right? So how far actually is it from your eye? >> Edited by beano500 on Friday 30th September 12:00
simpo two said:Yeah - I didn't explain my brainfog very well, did I?
...operative part being "should be". Don't think it will be in the real world.
Yeah but - if you project a 35mm slide onto a screen, get the picture sharp, then move a few inches backwards or forwards, it stays sharp!
In your projector screen analogy, whether you see the image as sharp depends upon the combination of eyesight and distance. Even 'though it's sharp all the time....
Now the question is this: with my lousy eyesight, will I judge the image to be in focus at a different point to you with your 20/20 vision?
beano500 said:
In your projector screen analogy, whether you see the image as sharp depends upon the combination of eyesight and distance. Even 'though it's sharp all the time....
Yes, the parallel assumes that you can see properly! Distance is not relevant. A picture on the wall stays sharp whether I'm 2 feet away, 10 feet away or in New Zealand! (Wow, relative sharpness and parallel sharpness
) beano500 said:
Now the question is this: with my lousy eyesight, will I judge the image to be in focus at a different point to you with your 20/20 vision?
If you can't focus on the screen, then you won't see the image as sharp, even if it IS sharp. My father did a lot of b/w developing/printing in the 50s and 60s and he was showing a friend how the enlarger worked. Friend said 'Aha, so it doesn't matter if the negative isn't sharp, you can make it sharp when you print it...'
That wasn't *your* father was it ? ;-)
simpo two said:
With the zoom, I could get noticably different results by changing the eye position relative to the viewfinder.
That sounds like a recipe for duff focusing if ever there was one, and might explain why you are getting such variable results. An image on a ground glass screen should be sharp regardless of eye position, no?
I would hazard a guess that the extra-long telephoto is putting to much of a demand on the camera's focusing aids and/or your eyes. If you want to use such focal lengths reliably, it might be time to move to an AF camera. Then you can let the camera take the strain and you can concentrate on other things like composition. AF also allows you to work much faster, if that's important.
Simpo,
I don't use the ground glass part of the screen very often. It's much too 'soft' IMO for anything other than studio work or when working with a known extended depth of field.
So the description of the problem relates directly to the split prism functionality and most obviously on the A1 body and not so much, if at all, to the other two. However, my experiments so far hardly amount to a scientific test!
It's a difficult thing to assess from results in the wild because there are so many other variables. The stuff I took at Donington recently, for example, was mostly with the F1n and the higher speed Vivitar Series 1 zoom working just about fully open using ISO400 film and lucky to get anything at 1/250th.
So speed was slow, lens was not at optimum, film would have a lot of grain and so on. Perfection or anything close is not guaranteed.
When I used the A1 with the 75-200 and 2x extender I would have f4.5 at best and plus 2 stops - so about f9 or so in real terms I guess. I ignored the underexposure warnings and was quite surprised to get any results at all - but it was a gamble to be taking moving targets, panning on a non parallel movement, lens wide open, shallow depth of field at 1/250th max.
Some shots were just wildly out of focus - my fault. Others were close but not quite there. With all the variables it is difficult to tell which had the most influence. But I didn't think it might be my pre-focus set except where I knew I had taken the shot when the cars were not at the focused position.
I'll go back and check the few statics I took with 35mm rather than digital, bit I don't remember them being a problem. Don't think I used the long lens combination for them though.
The eye position thing is rather specific in that the split area (on the A1 and AE1 at least, A1 worse than AE1) is half black and half clear with this lens combination fitted. Move a little and which is black and which is clear will flip. Sometime one can get just the right position for both halfs to be grey and so usable for the focus task. However that is probably not the right thing to do - it just highlights the nature of the problem.
The split prism is perfectly usable on the F1 so that eye position problem is not an issue, alignment with the prism is OK. But the focus difference between with and without specs still exists, albeit slightly and only with the extender in play, so far as I can tell at the moment.
The answer must be on the web somewhere - but should I leave that for a weekend task?
rude girl said:
Long Q, if you want to get technical on how your eyes are operating in these conditions, then there's a PHer called Kash you might speak to; his login is 968. He's a hospital eye specialist, and a really nice chap.
I've mailed him with a link to this thread.
Corinne
Good suggestion - thanks.
I think I need to get a fully assessed view of what the results are before getting too technical on the opthalmology front so will try to run some more tests.
It may all be down to how long I have been sitting/not sitting in front of a monitor before taking the shots!
rustybin said:
Do you get the same problem with the lens without the adapter or with other lenses? I am just trying to see if there is a way of eliminating the variables to see where the problem lies. Might it also be worth checking whether your current perscription is still appropriate.
Not as far as I can tell or at least not as obviously. One can of course get very fussy tryin to get alignement to the nearest nanometer or whatever ...
rustybin said:
Strangely my Father used to use three sets of glasses; reading, distance and photography. The photography set were a set generally about one perscription old that he swore got him better results. (However, he also reckoned he could hear better with his glasses on so may not be a wholly reliable source
Despite advancing age most of the time I have perfect vision at screen viewing distance. Teh rest of the range is less good ...
TO be fair my mild short sightedness has hardly varied at all (other than slight changes in astigmatism measurements over the years) since I was first kitted out in my teens. I can still feel comfortable with any old prescriptions I come across from time to time. The prescription is, I think, less than the inbuilt correction that many cameras have as an aid to sharpness. But realistically my understanding is that the split prism acts like a kind of range finder so in theory the ability to focus accurately, as per a ground glass screen for example, is less important.
These days I have reading glasses, though rarely use them. Only in poor light or if the old eye muscles are really tired - or one eye is and he other isn't, which produces odd results.
The speed with which the eyes refocus is much slower than it was - which is not useful for driving, especially at night but can be worked around. However it has been useful to appreciate the difference given that the majority of current drivers probably have the same limitations compared to the younger generations.
I could probably pass the number plate reading test without glasses. The astigmatism might be a hinderance depending on the characters on the plate. I could always tilt my head I suppose.
But I don't think any of that has much bearing on this since as I understand it most focusing screens are designed to simulate looking at an image about 3 feet away, in which case the issue is about the eye's ability to focus at 3ft. Or am I wrong in that?
So, wearing specs I tend to set the focus for the combination lens at a greater distance than not wearing specs.
Sitting at a monitor I cant wear specs and focus comfortably (or at all today!) at 3 feet. 5 to 6 ft seems about right but of course the characters are getting a bit small by then.
I'm wondering if that is the same effect through the lens (or its inverse) but more noticable for some reason with the extender.
As for your father's hearing - I could believe that! Direct transfer of sound waves from sensitive spectacle frames to the bone structure around the ear could have a distinct effect, though not always good. Or the pressure might move something in the structure of the ear passage that was effectively filtering certain frequencies.
Or it may indeed have been an imaginary difference.
Thanks for all the feedback everyone. Much appreciated.
LongQ said:
the split area (on the A1 and AE1 at least, A1 worse than AE1) is half black and half clear with this lens combination fitted. Move a little and which is black and which is clear will flip.
Actually I remember that happening with my old Ricoh XR7 and Vivitar Series 1 70-210 f3.5 when used with a T/C as well! I suppose the answer is that the split prism part was never designed to work with such focal lengths. Maybe you've simply run off the edge of what you can do with the kit you have. Physics etc!
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