35mm SLR Lens on DSLR. I'm confused.

[Martin Keene]

I currently have a 35mm Minolta SLR with a rather nice Sigma APO Macro 75-300mm lens.

I am thinking about a DSLR later this year and have been reading about the Sony A100 because the lens will transfer across. However I'm getting totaly confused with the focal lengths on DSLR's.

I can't work out if I will get the same picture with the 300mm lens fitted to the 35mm as I will on the DSLR, or whether the 300mm will become somthing more like a 200 or 400 when fitted to the DSLR.

Can somebody please attempt to explain it in English please?

[Gemm]

Focal length remains exactly the same, so it's still a 75-300 lens. But the sensor is smaller than the 35mm film, so the frame gets cropped making the images look like it's taken with a longer lens. If your camera's crop factor is 1.6x, 300mm is 'effectively' 480mm. Is it clear?

And be careful, old sigma lenses may need to be re-chipped to work on recent models.

Edited by Gemm on Sunday 17th February 11:23

[Martin Keene]

So if I buy a camera with 18-70mm lens, does the crop factor apply on this or has it already been taken into account. DSLR lenses appear to have short focal lengths than their 35mm cousins.

If the crop factor has been taken into account on the lense that comes with the camera, and my 75-300 effectivelt becomes 120-480, that means I'm going to have a 50mm hole in my focal range between lenses.

Hmm, annoying.

[miniman]

Can't comment specifically on the Sony range of lenses, but Canon have AF-S lenses which are DSLR-specific and with these, the crop factor is taken into account so 18-55 really is 18-55. The normal lenses are AF and they don't take the crop factor into account.

[horacethefrog]

Martin, as Gemm says, the focal length is the focal length, what you attach it to doesn't alter that. So all lenses attached to a camera with a crop factor of 1.6 will be affected in the same way i.e. multiply the focal length by 1.6 to calculate the equivalent lends on a film camera.

[horacethefrog]

Miniman, with all due respect, it's no wonder this guy's confused - from the Canon website "The EF-S 18-55mm f/3.5-5.6 is a standard zoom lens specifically designed for the EOS 300D digital SLR. Its effective focal length is equivalent to 29-88mm in 35mm film format."

[Martin Keene]

S0 regardless of the camera the 18-70 on the Sony will become 28-112, assuming a 1.6 crop factor. Interesting, so of the focal length remains the focal length, that means insteand of a range of lenses covering 28-300 as I have got at the minute, I will have a range of lenses covering 28-480mm with the DSLR.

Hmm, useful...

[miniman]

Martin Keene said:

S0 regardless of the camera the 18-70 on the Sony will become 28-112, assuming a 1.6 crop factor. Interesting, so of the focal length remains the focal length, that means insteand of a range of lenses covering 28-300 as I have got at the minute, I will have a range of lenses covering 28-480mm with the DSLR.

Hmm, useful...

Actually the crop factor on the A100 is 1.5x rather than 1.6x

[Simpo Two]

Exact figures aside, basically everything appears longer. So you'll get more telephoto but less wide angle - hence the need to have 18mm if you want the same field of view that you're used to at 28mm.

[flat-planedCrank]

If you are moving to dslr's then i'd recommend finding out which 3rd-party manufacturers support the lens mount of any camera you are looking at

I guess that is one of the reasons for Canon / Nikon are so popular, you can get lenses from Sigma, Tamron, Tonika...



Although the crop factor is 'bad' for wide angle shots, lenses such as Sigma's 10-20mm (about £280-290) have allowed cropped-sensor dslr's to regain that wide coverage


Cheers.

[Fordo]

Another thing worth noting is that the coating on digital lens is different to 35 mm lenses

- 35mm film isnt very reflective, but ccds do reflect a certain amount of light. as a result, most lenses designed for digital cameras have an antireflective coating on the arse end of the lens. 35mm lenses dont have this, so when used on a digital camera, in certain lighting conditions, you can get weird flares going on.

nothing wrong with using a 35mm lens on a dlsr, but its something worth remebering

[RobDickinson]

Bah not sure how much difference that makes, seems more like marketing to sell new lenses.

IMO if you have a few really cheap consumer zooms don't let that decide on the mount of your next camera unless your on a real budget and wont be buying new lenses.

You can always sell those cheapies and buy (used) cheapies on the new mount, or buy lenses with more appropriate focal lengths for cropped bodies.

[Martin Keene]

flat-planedCrank said:

If you are moving to dslr's then i'd recommend finding out which 3rd-party manufacturers support the lens mount of any camera you are looking at

I guess that is one of the reasons for Canon / Nikon are so popular, you can get lenses from Sigma, Tamron, Tonika...

It's a fair point. The Sony I'm looking at, because I can use my existing lens, uses a standard Minolta Dynax lens fitment.