[magkelly]

Okay, second question: if i had the chance ti get a used QS1 for $300 with the kit lens, would that be reasonable?

No, you could get one for a lot less in some places. I've seen quite a few sub $250 with the kit zoom. If you want the prime it would cost you nearer that.

[Mothballs]

My only remaining major concern is diffraction then, I suppose; The fastest lenses I have for long range ATM are the old Adaptall 200mm 3.5, which is the Adaptamatic basically, and a TAIR-3 300mm 4.5; The Q Seems to theoretically hit diffraction at what, f2.4-2.9, and the Q7 at around 2.8-3.4, which doesn't seem to exactly be helpful with my current lenses...

EDIT: This is all theoretical numbers, and I do expect real world Millage to vary; Sharpness of lenses vs limits by diffraction I do not think is a brick wall...

[Piotrek K]

My only remaining major concern is diffraction then, I suppose; The fastest lenses I have for long range ATM are the old Adaptall 200mm 3.5, which is the Adaptamatic basically, and a TAIR-3 300mm 4.5; The Q Seems to theoretically hit diffraction at what, f2.4-2.9, and the Q7 at around 2.8-3.4, which doesn't seem to exactly be helpful with my current lenses...

EDIT: This is all theoretical numbers, and I do expect real world Millage to vary; Sharpness of lenses vs limits by diffraction I do not think is a brick wall...

I have Adaptall-2 200/3.5 and it is not good on my Q. But the Tair can be good, I suppose in 4.5-5.6 range.

[vonBaloney]

I haven't tried it yet, but I would suspect the Tair to maybe not be the best on the Q -- mine at least is very sharp but a little too much fringing for the Q series I would suspect. As far as diffraction, with a very sharp lens you can get away with up to f/8 or even f/11 on the Q7 (and maybe f/5.6 on the original Q). But that's with the best lenses (like the DA*300) that are "that much sharper" than most others to begin with. But most lenses that are good enough to even be on a Q without looking terrible you can go to f/5.6 and it will be acceptable (since most K lenses will be getting sharper as they go up to f/5.6-f/8, if diffraction is kicking in it is somewhat canceled out) ...

[Tony Belding]

My only remaining major concern is diffraction then, I suppose; The fastest lenses I have for long range ATM are the old Adaptall 200mm 3.5, which is the Adaptamatic basically, and a TAIR-3 300mm 4.5; The Q Seems to theoretically hit diffraction at what, f2.4-2.9, and the Q7 at around 2.8-3.4, which doesn't seem to exactly be helpful with my current lenses...

Somebody I hope will correct me if I'm wrong but. . . . When using adapted lenses with their longer focal lengths, the aperture sizes are much larger -- not in f-number, but in absolute size -- and diffraction should be much less of an issue. Right?

[Mothballs]

Somebody I hope will correct me if I'm wrong but. . . . When using adapted lenses with their longer focal lengths, the aperture sizes are much larger -- not in f-number, but in absolute size -- and diffraction should be much less of an issue. Right?

F2 is f2 is f2. You can't get around that, really: the diffraction limit has more to do with pixel density. the k10d has a higher diffraction threshold than the K-50 For example. There's math involved and it's early here.

[6BQ5]

My only remaining major concern is diffraction then, I suppose; The fastest lenses I have for long range ATM are the old Adaptall 200mm 3.5, which is the Adaptamatic basically, and a TAIR-3 300mm 4.5; The Q Seems to theoretically hit diffraction at what, f2.4-2.9, and the Q7 at around 2.8-3.4, which doesn't seem to exactly be helpful with my current lenses...

EDIT: This is all theoretical numbers, and I do expect real world Millage to vary; Sharpness of lenses vs limits by diffraction I do not think is a brick wall...

Depends on the lens. Most native Q lenses work best wide open or just one or two clicks down from wide open. The 01 prime gives good performance all the up to f/4.

Pentax-01 Standard Prime 8.5mm f/1.9 (Pentax Q) - Review / Lens Test - Analysis

Sort of the same story for the 02 lens, except as you zoom in you should stay wide open.

Pentax-02 Standard Zoom 5-15mm f/2.8-4.5 (Pentax Q) - Review / Lens Test - Analysis

Diffraction and performance will depend a lot on individual lenses more so than the size of the sensor. The small sensor simply amplifies the effects because it is essentially cropping a small piece out from your image circle and you blow it up on your 21" screen. I think if your non-native lens works best at f/4 then you should use that setting if light allows. Forget about corner and border performance. It will all be cropped out. Concentrate on center sharpness.

[Mothballs]

Depends on the lens. Most native Q lenses work best wide open or just one or two clicks down from wide open. The 01 prime gives good performance all the up to f/4.

Pentax-01 Standard Prime 8.5mm f/1.9 (Pentax Q) - Review / Lens Test - Analysis

Sort of the same story for the 02 lens, except as you zoom in you should stay wide open.

Pentax-02 Standard Zoom 5-15mm f/2.8-4.5 (Pentax Q) - Review / Lens Test - Analysis

Diffraction and performance will depend a lot on individual lenses more so than the size of the sensor. The small sensor simply amplifies the effects because it is essentially cropping a small piece out from your image circle and you blow it up on your 21" screen. I think if your non-native lens works best at f/4 then you should use that setting if light allows. Forget about corner and border performance. It will all be cropped out. Concentrate on center sharpness.

So, RE Auto-Topcor 135mm 3.5? https://m.flickr.com/#/photos/74956563@N02/14679000250/

[6BQ5]

A big ol' film lens like that? Yeah, f/8-f/11 sounds about right and even that center could look fuzzy when cropped and zoomed in.

[Tony Belding]

F2 is f2 is f2. You can't get around that, really: the diffraction limit has more to do with pixel density. the k10d has a higher diffraction threshold than the K-50 For example. There's math involved and it's early here.

It's a ratio. F2 on a 100mm lens is 10X the size of F2 on a 10mm lens. I learned in my experience with telescopes that diffraction limits are based on clear aperture size, not f-ratios.

Pixel density is indeed a factor, though.

[Mothballs]

It's a ratio. F2 on a 100mm lens is 10X the size of F2 on a 10mm lens. I learned in my experience with telescopes that diffraction limits are based on clear aperture size, not f-ratios.

Pixel density is indeed a factor, though.

Care to expand on that? Because, to be fair here, the ratio of aperture size to lens length doesn't change when you crop, so I'm not sure I'm entirely following where you are going with this?

I enjoy learning things, and this is definitely learning and helping me make a decision.

[filoxophy]

Care to expand on that? Because, to be fair here, the ratio of aperture size to lens length doesn't change when you crop, so I'm not sure I'm entirely following where you are going with this?

I enjoy learning things, and this is definitely learning and helping me make a decision.

He's not talking about the focal ratio, he's talking about the physical aperture size. The Q 01 lens and the FA 43 Ltd are both f/1.9--but anybody can see that the 43's "clear aperture" is far bigger. This meaning of "aperture" is what we stargazers use, as it is the primary determinant of light-gathering ability (and yes, diffraction). The f-ratio is important in other ways, but not in the visual brightness of night sky objects.

Diffraction as it relates specifically for camera use is for somebody else to explain...

[Mothballs]

He's not talking about the focal ratio, he's talking about the physical aperture size. The Q 01 lens and the FA 43 Ltd are both f/1.9--but anybody can see that the 43's "clear aperture" is far bigger. This meaning of "aperture" is what we stargazers use, as it is the primary determinant of light-gathering ability (and yes, diffraction). The f-ratio is important in other ways, but not in the visual brightness of night sky objects.

Diffraction as it relates specifically for camera use is for somebody else to explain...

I am interested in your science and wish to learn more. Got anything useful for reading?

[filoxophy]

Quick formula relating telescope size (again, the "aperture" or physical diameter of the mirror/lens) and diffraction limits: The Diffraction Limit of a Telescopes

It is expressed as the smallest angular extent that can be distinguished in principal by the instrument, for example the minimum angular distance that two stars will appear separate rather than an elongated blob.

Regarding focal ratios and apertures, a quote from the following site: "Photographic f/stops are irrelevant to visual observers. Clear aperture and magnification determine visual brightness (exit pupil)."
http://www.chuckhawks.com/telescope_focal_length.htm

Magnification adds in the eyepiece of the 'scope, which can complicate things.

Anyway, I don't know if that's what you were looking for, but there it is. It's kind of funny how astronomers and photographers use the same terminology for their optics, but the practical considerations are very different!

[Scobra]

I am interested in your science and wish to learn more. Got anything useful for reading?

These two articles may shed some light on the subject (no pun intended)

F ratio myths in digital cameras and Depth of field myths in digital cameras