[MSL]

I know that the A50/1.7 and A50/2 have quite different optical formulas, and wide open these lenses behave quite differently as the A50/2 needs be stopped down quite a bit before it gets sharp. This comes from a detailed review of the lens that @UnknownVT posted several years ago (many thanks). The question I have is whether there would be any difference in the lenses when used with extension tubes for macro work, where ideally the lens will be stopped down at least to f5.6 if not more. Having built up a collection of teleconverters with A contacts for deglassing, I want to find the way to best make use of them. Certainly the A50/1.7 will let in more light for focusing, although I'm not sure how important that is. I know when I've shot macro using m42 lenses, it has sometimes been easier to focus with the lens closed down a bit if the situation was bright enough to allow it.

Even for ordinary shooting I wonder if these two lenses would show much difference once stopped down so any input welcome.

[old4570]

MAcro !


One really wants to close down that aperture for as much DOF as possible .. Even if you don't use a flash , you might want tot run F8 - F13 ..
Or go with flash assist and close the aperture all the way .
I need to buy a 2x tele converter with contacts and remove the glass for a Tube with contacts ... ( One of these days )


As to which lens to use , Ive used Ricoh lenses , F2 and F1.7 on top a macro tele converter and (??) cant tell the difference ..
Seriously , either lens @ f16 , is a 50mm lens @ f16 .. So unless there is something wrong with one lens , id say the difference would be like a few extra grains of sand on a beach .

[Not a Number]

If the extension tubes have the auto-stop-down lever the advantage of using K-mount lenses is you don't have to fuss with manually stopping them down. Unless the tubes have electrical contacts you will have to set the f-stop with the aperture ring on "A" lenses. This is moot with magnification over 1x as Pentax recommends using the lenses reversed for maximum sharpness. The Auto Bellows allow you to use a cable release to stop down the lens, even when reversed (mount specific e.g. K to K, M42 to M42).

The f/1.7 lenses have excellent flat field performance which is desirable for macro work. The Pentax Auto Bellows A manual warns against using the faster 50mm lenses such as the f/1.4 and f/1.2 as they do not have good performance for flat copy work. The A 50mm f/2.0 is ignored completely in the manual but charts for the M 50mm f/2.0 are provided. Charts are provided for the M and A 50mm f/1.7. Make of that what you will.

[Kerrowdown]

or look for an A50/1.7 for macro work

Have you considered a SMC Pentax-A 50mm F2.8 Macro, there is one for sale in the marketplace just now too.

[MSL]

Seriously , either lens @ f16 , is a 50mm lens @ f16 .. So unless there is something wrong with one lens , id say the difference would be like a few extra grains of sand on a beach .

Thanks that is good to know.

A Super Macro Takumar 50mm will cost abut the same as the A and can be used in Av mode. It's sharp form wide open (f4), and I find that manual stop-down operation can actually be more useful than wide-open focusing. With the de-glassed A contact teleconverters, you're going to get wrong aperture values anyway, since they take into account the light loss due to the glass.

I've got plenty of M42 lenses and extension tubes, and also a Vivitar 90/2 macro lens (but the focusing is so stiff it isn't any fun to use although I like the focal length). I've shot a fair bit of macro using these set ups, but there are times when I'd prefer to use the A modes if possible. I tend to shoot in brackets so account for possible errors in the metering.

Unless the tubes have electrical contacts

Yes they do which is why I bought the A type teleconverters for deglassing.

The f/1.7 lenses have excellent flat field performance which is desirable for macro work. The Pentax Auto Bellows A manual warns against using the faster 50mm lenses such as the f/1.4 and f/1.2 as they do not have good performance for flat copy work. The A 50mm f/2.0 is ignored completely in the manual but charts for the M 50mm f/2.0 are provided. Charts are provided for the M and A 50mm f/1.7. Make of that what you will.

That is useful info to know. I do have a SuperTak 1.4 that I may have tried for macro once or twice. I'd be interested in seeing those charts.

Have you considered a SMC Pentax-A 50mm F2.8 Macro, there is one for sale in the marketplace just now too.

I have LBA like most folks here, but the one thing I'm trying to avoid is buying another 50. If I bought (another) dedicated macro lens I'd probably get the Sigma 105 as that focal length better fits my needs (and then I'd also try to sell the Vivitar 90). I've seen what a few people do with that lens, and it looks like a joy to use. I also prefer doing macro with longer lenses, since I often try to capture bugs in the wild when they are moving

[Not a Number]

I'd be interested in seeing those charts.

You can download a copy of the manual from here:

Pentax auto slide bellows A, Pentax Slide copier A instruction manual, user manual

The close-up tables and lens discussion is towards the back of manual.

[MSL]

You can download a copy of the manual from here:

Fantastic. I scanned it quickly and I can see it has a lot of useful info. I also have m42 bellows and reversing rings and this guide talks about those options too. Thanks!