[derelict]

I shot Pentax for years. ist DS, then upped to the K7. I then had my daughter and switched to smaller, lighter, more portable M4/3 Olympus gear and sold all of my APSC gear. It's been great. However, I have now been shooting more film with my MX and using my Sony RX100 for my daughter. The Olympus is not getting used all that much so I am contemplating switching back to Pentax. I have some good 35mm lenses and if I could carry my MX and it's lenses along with a Pentax body, that would be seriously great. I cannot afford a K1 so I am considering a used K5IIs. What confuses me though is lenses on the APSC sensors. I take the focal length and multiple by 1.5 and get the new focal field of view, correct? Or do I take the 28mm of my K series lense and divide by 1.5 to get the new field of view equivalence?

I could spend the same amount of money and get a pro level zoom for my Olympus which would increase the likelihood of my carrying it around or buy an APSC K mount body and reduce the need to carry two platforms around.

[boriscleto]

You multiply by 1.5. So a 28mm lens on APS-C has the same FoV as a 43mm lens on 135 FF. A 35mm lens is "equivalent" to a 52mm lens etc.

The best advice is to not worry about "equivalence"...

[Rondec]

Basically, your APS-C camera won't see the whole image circle of your full frame lenses and so you will get an angle of view equivalent to a lens 1.5 times longer than your old lenses. You 28mm lens would end up like a 40-ish mm lens.

You would face the same thing with Olympus, where the crop factor is 2x. The one thing to mention about pro level zooms for Olympus is that while they are very nice, they do make your gear not quite as portable -- that is, they are pretty big. I like Pentax and shoot APS-C along with my K-1 and it works well, but Olympus makes nice cameras too. It just depends on what you are looking for.

Good luck!

[derelict]

I love my EM10. It's just that with my RX100 point and shoot, I find myself using it less and less. If I take my MX and a couple primes out, I wouldn't mind being able to just swap lenses over. Much better than carrying two different platforms. A 28 becoming something like a 42 is a bit of a detractor though. That means none of my lenses would work for landscape work really and that's a bummer.

[Na Horuk]

What confuses me though is lenses on the APSC sensors. I take the focal length and multiple by 1.5 and get the new focal field of view, correct? Or do I take the 28mm of my K series lense and divide by 1.5 to get the new field of view equivalence?

Here is how it works. All lenses have a focal length. This is a lens property and has nothing to do with the camera. The typical "film" is 35mm on the long side. But "crop cameras" have smaller sensor, so it is like cutting off the corners of that film. This makes the illusion that the Angle of view is different, less wide. Micro 4/3 and Q are even smaller than APSC. This is why smaller formats usually have lenes that are 5.6mm, 12mm... You can't find 5.6mm lens on 35mm Full frame, it would be insanely fisheye. But on a Pentax Q, its a sensible focal length for that sensor size.
All 50mm lenses will give you the same Field of view angle on a given camera. Its when you go from one sensor format to another that changes the apparent magnification/FoV.

This mean that if you like the Field of view of a 50mm lens on your Full frame/film camera, you need a 35mm lens on your APSC camera (35mm*1,5=52,3 which is about the same as 50). But you can still use FF lenses on APSC sensor camera. This is why old lenses like K or M or A or F or FA series all work fine on APSC cameras today.

I could spend the same amount of money and get a pro level zoom for my Olympus which would increase the likelihood of my carrying it around or buy an APSC K mount body and reduce the need to carry two platforms around.

I would always avoid having more than one system. Its confusing and expensive. You can get camera like Pentax K-S1 and it is super small. Add lenses like DA 21mm, DA 40mm, DA 70mm or DA 20-40mm limited and you have a great kit with lots of character, really great image quality, DSLR controls, in a really small package. Pentax gear is pretty compact compared to others, and it is reasonably priced.
Another advantage of Pentax K is that it can mount pretty much any Kmount lens without need of adapter. So you can put that K 28mm on K10D or K-S1 or K-3 or even K-1. On K-1 it will look the same as on film (perhaps more resolution), but on APSC cameras it will not look as wide.

[derelict]

Here is how it works. All lenses have a focal length. This is a lens property and has nothing to do with the camera. The typical "film" is 35mm on the long side. But "crop cameras" have smaller sensor, so it is like cutting off the corners of that film. This makes the illusion that the Angle of view is different, less wide. Micro 4/3 and Q are even smaller than APSC. This is why smaller formats usually have lenes that are 5.6mm, 12mm... You can't find 5.6mm lens on 35mm Full frame, it would be insanely fisheye. But on a Pentax Q, its a sensible focal length for that sensor size.
All 50mm lenses will give you the same Field of view angle on a given camera. Its when you go from one sensor format to another that changes the apparent magnification/FoV.

This mean that if you like the Field of view of a 50mm lens on your Full frame/film camera, you need a 35mm lens on your APSC camera (35mm*1,5=52,3 which is about the same as 50). But you can still use FF lenses on APSC sensor camera. This is why old lenses like K or M or A or F or FA series all work fine on APSC cameras today.


I would always avoid having more than one system. Its confusing and expensive. You can get camera like Pentax K-S1 and it is super small. Add lenses like DA 21mm, DA 40mm, DA 70mm or DA 20-40mm limited and you have a great kit with lots of character, really great image quality, DSLR controls, in a really small package. Pentax gear is pretty compact compared to others, and it is reasonably priced.
Another advantage of Pentax K is that it can mount pretty much any Kmount lens without need of adapter. So you can put that K 28mm on K10D or K-S1 or K-3 or even K-1. On K-1 it will look the same as on film (perhaps more resolution), but on APSC cameras it will not look as wide.

Yeah, I understand all of that. I could not figure out the equivalent FoV using my A and M lenses on something like a K5IIS. The one thing I do not want to do is invest in APSC lenses that will not work with my MX 135 body.

[pathdoc]

Yeah, I understand all of that. I could not figure out the equivalent FoV using my A and M lenses on something like a K5IIS. The one thing I do not want to do is invest in APSC lenses that will not work with my MX 135 body.

All of the APS-C lenses lack an aperture ring, so quite aside from the field of view, NONE of them will work on your MX. They will default permanently to whatever the minimum (narrowest, fully closed down) aperture is.

It's a shame, really, because some of these lenses - especially the DA Limited primes - are perfect matches in size for a body of MX proportions. It's a good thing the reverse is true - fantastic, actually.

The K-5 series were and are wonderful cameras. The only thing they will not do, though, is take the new generation of PLM/KAF4 lenses, so if you get one you might be buying into long term obsolescence. K-5 owners have been petitioning Pentax for a firmware upgrade in this regard but there are not even whispers of such, while even the lower-end K-50 recently got one. So think a bit and consider a used K-3 instead. I am a proud K-5 (and MX) owner myself, and until now I have hitherto been unhesitant in recommending it as a secondhand option... but now I must issue that caveat.

[surfar]

The Pentax Camera Lens Compatibility Chart

[victormeldrew]

Yeah, I understand all of that. I could not figure out the equivalent FoV using my A and M lenses on something like a K5IIS. The one thing I do not want to do is invest in APSC lenses that will not work with my MX 135 body.

The modern DA series of lenses are designed for the smaller APSC sensors and so may not be compatible with full frame/35mm cameras. But full frame lenses will work on either.

[pepperberry farm]

You multiply by 1.5. So a 28mm lens on APS-C has the same FoV as a 43mm lens on 135 FF. A 35mm lens is "equivalent" to a 52mm lens etc.

The best advice is to not worry about "equivalence"...

^^this^^

"equivalence" is something that bothers you when you aren't shooting.... best solution is to get out and shoot....

[Na Horuk]

Yeah, I understand all of that. I could not figure out the equivalent FoV using my A and M lenses on something like a K5IIS. The one thing I do not want to do is invest in APSC lenses that will not work with my MX 135 body.

Ah. DFA lenses will cover the image frame of film and FF, as will all series before DA. Some DA lenses also have large enough image circle. Check reference threads and tools:
DA lenses on Full Frame: Test Shots thread - PentaxForums.com
PENTAX K-1 Laboratory | PENTAX K-1 Special site | RICOH IMAGING
Pentax Lens Search | PentaxForums.com

BUT another problem is Aperture ring. Most modern Pentax lenses do not have one, so they cannot be used normally on cameras without auto-aperture. Third party lenses like Samyang and I think a lot of Sigma lenses still have aperture ring. Samyang is a good choice, because they are modern optics but made for Manual focus (but not all their glass is made for FF, and you have to be sure to get Kmount lens, not Canon Nikon Sony or other. Check per lens)

[stevebrot]

I could not figure out the equivalent FoV using my A and M lenses on something like a K5IIS.

Here is a quick cheat sheet that does not use unfamiliar jargon or math:

APS-C Guide to Focal Lengths:

• Ultra-wide: 16mm and shorter
• Wide: 17mm ---> 24mm
• "Normal": 28mm --> 35mm
• Classic portrait: 40mm --> 60mm
• Medium tele*: 70mm --> 110mm
• Long tele: 120mm --> 200mm
• Ultra tele: 250mm and longer

Expectations regarding working distance, DOF, appropriate subjects and "other stuff" follows the class of lens. In regards to cross-operability, any Pentax lens in the F and FA series will be fully supported on all Pentax dSLRs and your MX. A-series offer full automated exposure support, somewhat lower P-TTL flash compatibility, and no auto focus. The earlier K and M series were designed to work with your MX, but are a little clumsy on the dSLRs in that only stop-down metering is supported.


Steve

(...has several K-mount film bodies and happily uses the full collection of K-mount lenses (-2 without aperture rings or adequate image circle) on both those and the K-3...)

* Many (most?) lenses labeled tele on this list are done so out of convention. Few actually feature telephoto design.

[DeadJohn]

If you want to compare fields of view between APS-C and 4/3, scale by 1.5 and 2.0 respectively.

Let's say you have a 30mm 4/3 lens and want something with the same view on APS-C. 30mm * 2.0 = 60mm "equivalent". 60 / 1.5 = 40mm lens on APS-C.

It doesn't matter whether the 40mm lens is only APS-C or full frame. Every 40mm lens on APS-C will have the same view as a 30mm 4/3 lens.

[Cthulhugan]

Some of the later Pentax film SLRs can set the aperture from the body, allowing use of a lens without an aperture ring in all modes. All Pentax film SLRs that take A-series lenses can set the aperture in Program or Shutter Priority mode. Some of these cameras can be had for little cost.

[Rondec]

If you get a K5 II, just plan to continue using your old lenses, but supplement them with a cheap zoom that would cover the wider angles that you don't have already. Something like the DA 18-135 or the Tamron 17-50 f2.8 would work nicely and they aren't very pricey. For that matter the kit lens (18-55) is decent and that is really cheap.