pentax M vs pentax A

what's the difference on DSLR? (k100D)?
thx

The simple answer is with M you have to select the Aperture on the Lens instead of on the menu and work in Fully Manual (M) mode.
...There is a catch though with metering (see below)

With A, you can use Aperture Priority (Av) and Shutter Priority (Sv) modes, so the only thing you have to do manually is the Focus. Apart from that, they are exactly the same as any modern lens.

The catch with "M" lenses is getting the camera to work-out what Shutter Speed you need. This is where you use the Green Button to do "Stop Down Metering" - which whenever it is described sounds horribly complicated, but basically :

- you press the green button
- camera takes a meter reading
- camera sets the shutter speed
- you can now take a picture(s)


If you haven't used either before, I'd suggest getting an A series lens before moving on to a M series. You can turn an A into a M by moving the aperture ring to a fixed value instead of Auto, to get the hang of the Green Button. I'd also only bother with Primes when it comes to old lenses, forget the Zooms - modern ones are (generally) superior...


p.s.
The other difference is that "A" series lenses tend to cost a lot more than "M" series, because the manual metering scares people - even though some of the M lenses are better than the later A's!

Cool thx for that. A few years ago I bought a M 50mm but it didnt work on my film SLR, so went back to the shop and bought an A 50mm instead. For that reason I assumed M wouldn't work on my DSLR - I sold my A F2 50mm 2 years ago but after reading a few comments about how great these lenses are I kind of want to give it another try (never used it on my DSLR).

Does the F1.4 F1.7 F2 difference justify the price difference? If I recall most of the time when being outside on a sunny day I couldnt use the F2 as the camera would need to shoot at 1/50,000s or so and think the max was like 1/30,000s... does that make sense?

Remember you can now adjust the ISO on your camera as well, maybe you were using some high iso film?

The A-50/1.7 is a fantastic lens, really great to play with, loverly feel, and so small. The 1.4 has a big price premium which unless you want a razor-thin Depth of Field is a lot to pay! F2 is common as muck, very cheap, and nowhere near as good as either the 1.7 & 1.4 by all accounts.

I just had a very quick look - I took some F 1.7 shots outdoors in blazing sunshine at midday with the A-50/1.7 at ISO 400 and 1/5000 sec with a CPL filter. Or some extremely low-light shots at ISO 1600 and 1/30 sec (no filter). Your K100d I think would like a lower ISO than that, but hope that gives some indication of the shutter speeds...

the K100D cant go under 200ISO

ok i will see if i can find a cheap A F1.7 on ebay, i am all excited now!!

thx
P

I could be wrong, as I don't have the K100D now, but if you select Auto for the ISO setting I thought ISO100 was the default.

the base ISO on the 6MP sensor (as used in the *ist series and the K100/110) is 200, it can't go lower than that.

Outside on a sunny day you may find that f/2 is unusable, but indoors or at night that extra stop will suddenly be a godsend. I have owned several 50s, from the M f/2 to the FA f/1.4 and all have been excelent in terms of image quality.


One point to note re flossies otherwise excelent answer though, Sv is Sensitivity Priority and isn't available on the K100D, I think Tv (Shutter Priority) is what was meant. P (program) and the scene modes should also be available with an A series lens, not sure if Auto-Picture will work though as it uses lens information which is only provided by the FA series lenses.

One last thing: metering with M series lenses tends to be unreliable compared to the A series. For static shots this isn't a problem (shoot, check histogram, adjust, reshoot...) but for grab shots etc. it is a pain.

The other possibility is to buy a M42 lens which can be used in Av mode as well as you can just shut the aperture down using the "Auto Manual" switch on the lens.

Best wishes, Kris.

Ah, sorry for any confusion - Shutter Priority (Tv) is what I meant, I just couldn't remember what its abbreviation was, so looked at my camera in a hurry and read the wrong label off the dial.

[quote:3496ace15f="womble"]One last thing: metering with M series lenses tends to be unreliable compared to the A series. For static shots this isn't a problem (shoot, check histogram, adjust, reshoot...) but for grab shots etc. it is a pain.

This varies depending upon the camera body and focussing screen used - metering with the early *ist bodies and with the K-7 using M lenses seems to me to be more accurate than some of the others - I know of people who installed *ist focussing screens in their K10D/K20D bodies to get around this problem.

One other issue that is worth a mention is build quality for the SMCA f1.7 lens, which does not quite measure up to that the SMCM. The SMCA includes more plastic components, including in the aperture mechanism which can become notchy and unpleasant as the lenses get older. This is not an issue if you only intend to use the lens at its "A" setting and use the e-dial on the camera to stop it down. It is an issue if you want to use the aperture ring on the lens - you'd need to make sure you get a good one.

I found this to be true with the K10D and K20D, what I tend to do is meter the scene at wide open aperture in manual (M), then as I stop down to the taking aperture I just adjust the shutter speed accordingly. It's something that you get used to when you've worked with manual only cameras for years.

Regards,

John

thx and thanks!
i am aiming for an A as wouldnt bother doing everything manually (my gf already hates me for taking 10 sec to take a picture, i cant even imagine having to do the metering )

still not sure whether i'll get the 1.7 or 2, depends on what i'll find (and what price!). and yes I can confirm on the K100D 200ISO is the minimum

thanks guys
P

Advantages of A-series:
*Aperture controlled on camera (dials!) rather than the aperture ring
*The viewfinder is always bright for easier manual focusing (e.g. on an M 50 1.7 if you stop down to f5.6 the viewfinder will get darker, on an A 50 1.7 it won't)
*Supports auto P-TTL flash (ie you set the aperture and shutter speed you want, the camera works out how much flash power to use for proper exposure) rather than having to set the power manually (on a flashgun) or not use flash at all (the built-in flash, which doesn't have manual power settings)

The viewfinder stays bright on all K mount lenses - the camera stops them down as part of the picture taking process. M42 lenses don't have this coupling (at least, not one which works on K mount bodies).

The main advantages I find are that you can use Program mode and the metering is a bit more stable with the A series. I find that stop down metering with the K and M series is pretty much on the money down to f11 or so - go smaller and it starts underexposing.

I have used manual cameras (or cameras in manual mode) for years. If they had been as far off with the metering as my K20D is with older glass I would have been quite upset. Slides come in at about 25p a picture... I used my ME Super (in manual) with Kodachrome 64 until I literally wore the camera out. I hoped that fitting the katzeye screen might improve matters but it didn't, and I also find that every manual lens behaves slightly differently. The Vivitar 28mm close focus (Komine) lens is, for example, badly out at all apertures.

Best wishes, Kris.