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02-15-2009, 11:34 AM   #16
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It should be easy to make one using a rear lens cap, plastic tubes of the correct ID, and some glue.

Dave

02-16-2009, 02:16 AM   #17
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QuoteOriginally posted by Luciferase Quote
Oh, ya, sorry I was referring to a telescope eyepiece (barrel diameter of 1.25"). There are plenty of eye relief ranges for them (for as low as 5mm to as high as 25mm). There are even those with zooms (8-24mm).

Such as:
Super Zoom Plossl Eyepiece 8-24mm 1.25" Telescope New - eBay, Telescopes, Binoculars Telescopes, Photography. (end time 16-Feb-09 09:00:00 AEDST)

As for custom design and drill work. I only wish I have that experience on metal work and know how.

Cheers.
I know what you mean and you won't get that off the shelf. There is no commercial adapter available to use a standard astronomical (or any other) eyepiece, whatever barrel size, on a K-mount lens. There is no way around machining something or trying to build it from different parts.

Ben
02-16-2009, 02:17 AM   #18
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QuoteOriginally posted by newarts Quote
It should be easy to make one using a rear lens cap, plastic tubes of the correct ID, and some glue.

Dave
You also need some kind of drawtube or - as I wrote above - a standard 1.25 inch helical focuser to focus the whole assembly.

Ben
02-16-2009, 02:20 AM   #19
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QuoteOriginally posted by Lowell Goudge Quote
vivitar makes one or did many years ago

If I can find mine I will post a photo
I know the Vivitar telescope eyepiece. It has a fixed 10mm eyepiece and that cannot be exchanged with another one as the thread opener wishes. I also contemplated the Vivitar adapter once, because I though, if I remove the eyepiece part, I could replace it with a standard 1.25-inch drawtube or whatever, but the plastics of the Vivitar is very brittle and does not lend itself to rework anything mechanically.

Ben

02-16-2009, 06:21 AM   #20
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Thank you everyone for their advices.
02-16-2009, 07:08 AM   #21
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QuoteOriginally posted by Ben_Edict Quote
I know the Vivitar telescope eyepiece. It has a fixed 10mm eyepiece and that cannot be exchanged with another one as the thread opener wishes. I also contemplated the Vivitar adapter once, because I though, if I remove the eyepiece part, I could replace it with a standard 1.25-inch drawtube or whatever, but the plastics of the Vivitar is very brittle and does not lend itself to rework anything mechanically.

Ben
perhaps not flexible, but it does convert a 400mm tele into a 40 power spotting scope.

Trust me, you can't easily use more.

I also have a celestron C90 (1000mm F11) and I have 25 and 9mm eye peices plus a 2x barlow.

beyond 50 times, (2x plus 25mm) vibration is so bad on a tripod that you need to really be on a windless day, and at 200x (9mm plus 2 x barlow) the field of view is so narrow that you can view jupiter and saturn but they move across the field of view in 20 seconds, making a motorized equatrial mount a necessity
02-16-2009, 07:50 AM   #22
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Perhaps you could marry a 1.25" - 2" eyepiece adapter to an adjustable, K type extension tube.

I think this will be easy to do and will require little or no machining. The inner diameter of the 2" end of the eyepiece adapter should be just right to slip over the male end flange ears (1.91") of a K type extension tube where it may be glued in place or otherwise secured.

The 1.25" ID end of the eyepiece adapter is then available to accept your eyepiece.

In the worst case, the brass ears of the extension tube's male K end may have to be filed a little so it'll slip into the eyepiece adapter.

On edit: it turns out the inner diameter of the 2" end of the adapter tube is threaded to accept 48mm threads. This implies that the K-mount flanges will self tap into the adapter.

This will work.

Dave

PS the real image of the Pentax primary lens is 45.46mm behind the lens' mating surface for infinity focus. Where should the 1.25" eyepiece be positioned? (I may try this but don't know how to position - or select- the eyepiece!)

Last edited by newarts; 02-16-2009 at 08:08 AM. Reason: new info about eyepiece adapter
02-16-2009, 08:35 AM   #23
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QuoteOriginally posted by Lowell Goudge Quote
perhaps not flexible, but it does convert a 400mm tele into a 40 power spotting scope.

Trust me, you can't easily use more.

I also have a celestron C90 (1000mm F11) and I have 25 and 9mm eye peices plus a 2x barlow.

beyond 50 times, (2x plus 25mm) vibration is so bad on a tripod that you need to really be on a windless day, and at 200x (9mm plus 2 x barlow) the field of view is so narrow that you can view jupiter and saturn but they move across the field of view in 20 seconds, making a motorized equatrial mount a necessity
Hi Lowell, yes, I know that - I have been in astronomy for more than 30 years and have my own observatory with five scopes up to 3000mm primary focal length... (you couldn't know that).

regards
Ben

02-16-2009, 08:40 AM   #24
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QuoteOriginally posted by newarts Quote

PS the real image of the Pentax primary lens is 45.46mm behind the lens' mating surface for infinity focus. Where should the 1.25" eyepiece be positioned? (I may try this but don't know how to position - or select- the eyepiece!)
Usually the eyepiece focus is positioned right where the telecope focus is, only then you get the parallel rays your eye need for refocusing (the thirs lens in this game). This is the problem with an eyepiece adapter on a lens: the drawtube or focusing unit has to have quite a long travel to accept the different eyepieces.

Otherwise your advice with the variable extension tube is a good idea. Pentax once made the helicoid extension tube, which is a fine piece of equipment, though very rare now. But one could also assemble a focusing unit from the Baader Planetarium T2 system. BUT everything available on the market will have the K lens mount, not the body mount, which one needs here.

Ben
02-16-2009, 08:57 AM   #25
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QuoteOriginally posted by Ben_Edict Quote
Usually the eyepiece focus is positioned right where the telecope focus is, only then you get the parallel rays your eye need for refocusing (the thirs lens in this game).
Is there a standard dimension from a place on the eyepiece and its focal point or is that part of the eyepiece specification or what? I know nothing about customary practices for telescope equipment, but such things are likely set in stone.

QuoteQuote:
BUT everything available on the market will have the K lens mount, not the body mount, which one needs here.
That's the reason to use an extension tube; it has both male (lens) and female (body) ends. The female end accepts the lens (like a camera body does) and the male end serendipitously just fits into the 2" end of a standard 1.25/2 eyepiece adapter. This leaves the 1.25" ID end of the adapter free to accept an eyepiece.

Dave
02-16-2009, 12:39 PM   #26
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QuoteOriginally posted by newarts Quote
Is there a standard dimension from a place on the eyepiece and its focal point or is that part of the eyepiece specification or what? I know nothing about customary practices for telescope equipment, but such things are likely set in stone.
Usually (not always, though), the focal plane of the eyepiece is where you will find the field stop (a fixed round baffel ring, quite like the aperture blades of a photographic lens, but with a fixed size.

QuoteOriginally posted by newarts Quote
That's the reason to use an extension tube; it has both male (lens) and female (body) ends. The female end accepts the lens (like a camera body does) and the male end serendipitously just fits into the 2" end of a standard 1.25/2 eyepiece adapter. This leaves the 1.25" ID end of the adapter free to accept an eyepiece.
You are ofcourse right - I simply did not really think about the extension tube you suggested. SOmetimes it would be better to delay a reply...

Ben
02-16-2009, 01:19 PM   #27
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I recall seeing a fixed 10mm eyepiece setup for k-mount lenses, might have been at B&H.
Short of ordering mount parts, I pieced together something quick.

1st, setup was easy and mechanically solid to some degree.
500mm f8, T-mount mirror lens coupled to reversed t-mount adapter and a 25mm eyepiece.
Had plenty of focusing range, upside down and reversed image of course. Optically however, it sucked.

2nd, was a Pentax 70-210mm f4 with gutted 2X converter for holding the eyepiece in place. Had just enough focusing range to get by, image looked very good with 25mm ocular and usable with 10mm one.

But similar results can be obtained by using even a cheap spotting or telescope.
So, IMO, not worth the hassle, save your lenses for your camera.

Cheers, Mike.

edit; the setup I had seen was for M42.

Last edited by Ex Finn.; 12-29-2013 at 10:40 AM.
02-16-2009, 05:28 PM   #28
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QuoteOriginally posted by Luciferase Quote
Had anyone seen any adaptor that could convert a K mount lens (not a m42) to a 1.25" eyepiece holder?

If so, where could I buy one?

It's going on my tamrom 70-300mm.

Thanks
Web Cam Adapter - Mogg Adapter
Made to order, should also work with eyepiece, might be worth checking out.

Any kiwis, I mean, Aussies, know of this guy?
1.25-PentaxK
This adapter connects a Pentax K bayonet SLR lens to a 1.25" focuser tube with three set screws. The back focus is adjustable via the set screws holding the camera 1.25" tube. The range of adjustment may not allow all cameras to achieve focus so please check that this adapter will work for your particular camera. The mount has a 1/4-20 mounting point so that it can be fixed to a tripod mount.

Cheers, Mike.

Last edited by Ex Finn.; 02-16-2009 at 05:30 PM. Reason: nope
02-17-2009, 06:37 AM   #29
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QuoteOriginally posted by Ben_Edict Quote
Hi Lowell, yes, I know that - I have been in astronomy for more than 30 years and have my own observatory with five scopes up to 3000mm primary focal length... (you couldn't know that).

regards
Ben
That is one big lens! Man, I wish I could afford one and a place to accommodate it. But so much light pollution in suburban Sydney
QuoteOriginally posted by newarts Quote
That's the reason to use an extension tube; it has both male (lens) and female (body) ends. The female end accepts the lens (like a camera body does) and the male end serendipitously just fits into the 2" end of a standard 1.25/2 eyepiece adapter. This leaves the 1.25" ID end of the adapter free to accept an eyepiece.

Dave
I had the macro extension tubes in mind before this post and tested it to see whether it’ll fit with the 2” end of a 2” to 1.25” adaptor. My macro tubes have about ~60mm ID, so there remains a gap for this setup.

QuoteOriginally posted by Ben_Edict Quote
You are ofcourse right - I simply did not really think about the extension tube you suggested. SOmetimes it would be better to delay a reply...

Ben
Yep, once the adaptors are in place, we could simply add rings of extension tube for right focus.

QuoteOriginally posted by Ex Finn. Quote
I recall seeing a fixed 10mm eyepiece setup for k-mount lenses, might have been at B&H.
Short of ordering mount parts, I pieced together something quick.

1st, setup was easy and mechanically solid to some degree.
500mm f8, T-mount mirror lens coupled to reversed t-mount adapter and a 25mm eyepiece.
Had plenty of focusing range, upside down and reversed image of course. Optically however, it sucked.

2nd, was a Pentax 70-210mm f4 with gutted 2X converter for holding the eyepiece in place. Had just enough focusing range to get by, image looked very good with 25mm ocular and usable with 10mm one.

But similar results can be obtained by using even a cheap spotting or telescope.
So, IMO, not worth the hassle, save your lenses for your camera.

Cheers, Mike.

edit; the setup I had seen was for M42.
But IMHO, lens coats are by far more superior than telescope ones?
Although they wouldn’t have as much light gathering power, but in terms of CA, shouldn’t they outperform single lens spotting scope in daylight?
Is that 500mm a cheaper generic brand? (That’s similar to the setup I had in mind)
As for the good quality of the 70-210mm, that is exactly what I wanted but not a permanent fix setup. Whereas an adaptor that can be mount to ANY lens for a quick conversion to a telescope.
If one adaptor is the price of a cheap spotting scope, having it would double the use of your lens collection than just photos, right?
QuoteOriginally posted by Ex Finn. Quote
Web Cam Adapter - Mogg Adapter
Made to order, should also work with eyepiece, might be worth checking out.
Cheers.
02-17-2009, 06:54 AM   #30
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The better scopes have coatings as good, if not better than anything out there.
For astro work, aperture rules.
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