M42 - Peleng

Hi

I have a Peleng 8mm with a M42 adapter, now the lens is fully manual which is not much of a problem , how ever one thing I noticed is that the focus indicator does not work with this lens attached, and I am wondering If this has to do with the M42 adapter; could it be that the adapter is just a mm too long? Are there different M42 adapters? ( I saw that Steve in another forum called it M42-PK)

Also another question; to be able to use the green button, i have read that apart from being in M mode, the aperture should be wide open, so at f/3.5 with the Peleng, this is a shame cuz as we all know the all around sharpness decreases.. so does it have to be at f/3.5 or could i use it at f/17?

All this said I have managed to take good pictures with it but would like to know the correct way as to not waste opportunities

Thanks
pano

There is only one type of M42 adapter to use screw fit lenses on K fit bodies, so that is not the problem. I think the problem is that an 8mm lens has so much depth of field that it will be impossible to focus it with any accuracy on a ground glass viewfinder screen. Focusing aids will probably not help much either. Setting the distance by guessing should not be too much of a problem.

As regards metering, are you using this on a *istD? If so, you need the firmware upgrade to make the lens properly compatible - others who know more about this have posted the info on this forum and perhaps someone can repeat it here?

HI

Yeah i was not asking how to meter it, just if the aperture set of the lens made any difference as it apparently does (from what i read on another post) also each time i read about it there are small facts which are forgotten

The explanation of the focusing would not explain why it does not focus objects at close range (or give the signal)

Any how it would be handy if some one had the lens, as I also seem to get a white foreground when used with a flash ??

Thanks anyway
pano

Regardless of whether we are using lenses on a traditional film or a digital body, the laws of optics do not change. So an f4 lens will always be an f4 lens in every respect, although the smaller format of digital will inevitably mean nmore depth of field, for example.

You mention flash, and with an 8mm lens if subjects are close to the camera it will be especially easy for them to become washed out ("white"?) because of over exposure. An 8mm lens is a very extreme case and will need very careful handling indeed.

Still, the results could also be very dramatic, and I hope you get much enjoyment out of using the lens!

The smaller "format" of digital will mean a narrower angle of view. I don't see how it can affect the depth of field.

It doesn't in one sense, but it does if you consider what happens to the end effect. For example, as a consequence of format size the standard lens of a 110 camera is 24mm, and has the depth of field of a 24mm lens. The standard of a 35mm camera is 50mm for a similar angle of view and has the DOF of a 50mm lens, which is less than a 24mm.

On the digital, the 50mm lens appears to have the angle of view of say a 75mm, but it still has the DOF of a 50mm, just like any other 50mm lens....Converslely, a 50mm on a Pentax 67 would definitely be a wide angle, but with inherently less DOF that we would be used to on a 28mm on 135.

This is complicated by bringing in the concept of magnification ratio, which is what DOF really relates to, but the general principle above is what seems to happen in a practical sense.

Do you know of any sites that demonstrate this phenomenon with pictures?

I am not wholly convinced by the DOF argument, and would be interested to see two pictures side by side of the same subject shot from the same position at the same aperture with lenses that have an equivalent field of view on the two cameras (35mm and APS-size). A 77mm and a 50mm would probably be near enough.

One reason why the apparent depth of field on a long lens is shallow is because in fact it is covering a much greater distance. Put a smaller focal length lens on a camera with a smaller frame size, and I don't see why you won't get the same depth of field.

George

Whatever have we started? This is very complex if it is to be absolutely correct, but say for instance you have a 28mm lens and fill the frame with a subject. Then take a 100mm lens and fill the frame with the subject. In both cases, as the image size on the film (i.e., the magnification ratio) are the same, the depth of field will be exactly the same for a given aperture. However, the perspecrtive will be different because you will be very close with the 28mm and further away with the 100mm.

Now it is well known that there is less apparent depth of field with large format cameras than with say 35mm ones. This is because a large format standard lens might be, say, a 210mm and a 35mm one will be around 50mm. 210mm lenses have less inherent depth of field than 50mm ones.

You can find out about these matters in detail in books on photographic optics, and in less deatail in the better brochures such as the Pentax publication "The Eyes" (probably long out of print) and similar ones from Canon and others.

Otherwise, you can prove it with test shots, which I have done for some of my summer talks at ADAPS.

John

Do you have any side by side examples you can point to on a web site?

Same position, same subject, same aperture, same field of view, different focal lengths and different frame sizes so as to give the same AOV?

There's just too much optical theory to absorb for an old brain, and much of what is written doesn't address the question of what happens when you use different frame sizes with the same AOV.

I do, but I haven't got time just now to put them together properly.

But to take the last point about different frame sizes (and I assume you are thinking of Digital SLRs in this context) then the same applies as would do different film formats. I have chosen widely separated formats in my answer above just to make the difference clearer. If we go to an absolute extreme, then a Minox standard lens for 8x11mm negatives is a 15mm, which has tremendous depth of field and requires no focusing, pretty much as you would expect from the SMC Pentax 15mm f3.5....But in the Minox case the angle of view is a standard lens and in the Pentax case it is an Ultra-Wide. But it is still a 15mm lens in both cases.

I will have a look at my Powerpoints and see if there is a sequence I can send you, perhaps on CD or perhaps by e-mail depending on the file size. Sorry I can't look into it for a day or two, but I will look.

Thanks, John.

Don't go to any trouble. I was hoping you might be able just to point me to something. I've been looking, but can't see anything that gives a clear side by side example.

HI

Interesting theory of the DOF

Now i just got ahold of an old pentax SuperA, and to my (not) surprice i could not get the Peleng to focus, THe Super A has one of those old focus systems with the circle and a middle line, and i can not get the lines straight in the middle..

What could i be doing wrong if any? Could it be the m42 screw that it is too long? help!

Pano

I think, as said before, that it is because there is so much depth of field that the focusing method is not reliable. You may have to estimate distances, but that will not cause much of a problem for the same reas0n - masses of depth of field.

Thanks john
You are right the pics come out alright, but i just can't get over this little technicality

Pano