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04-11-2015, 07:34 AM   #16
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QuoteOriginally posted by JimmyDranox Quote
In astronomy, aperture means the effective diameter of the light collecting element. Whether is a lens or a mirror. No relation to the F from photo. Also, in astronomy, F, or some time F/D, means the ratio between focal length and diameter, in the same way as in photo, with the difference that you can't change the F, because their is no diaphragm.
Y
The 560mm/5,6 is a lens with a 100mm effective diameter, at least in theory. I never saw one in reality. So, the DA 560mm/5.6 must be better in IQ that this spotting scope with his 65mm diameter.
Thanks. So this would make it an f 13 or something along that line. Not to fase for photography, but on a sunny day no issue.

04-11-2015, 08:35 AM   #17
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I don't know the native focal length of those spotting scopes. Sometime, for this type of instruments, the camera adaptor have active optical elements, and they act like focal extenders. Other time, are only mechanical connectors. For this case, it has optical power for sure. In the astronomers world, many people makes all kind of transformation, including adapting camera directly to the instruments, modifying the optical pass and more like this. Of course, the simplicity of the telescopes, alow this.
04-11-2015, 09:10 AM   #18
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QuoteOriginally posted by thibs Quote
Yep, I remember all Pentax astronomy products were basically canceled/sold.
Hopefully, I remembered badly. Eyepieces are indeed much known for quality (and price).
Nope; the XW eyepieces, which are top of the line are still available. I have 3 of them.

https://astronomics.com/pentax-xw-eyepieces_c80.aspx
04-11-2015, 10:31 AM   #19
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Spotting scope different

QuoteOriginally posted by JimmyDranox Quote
In astronomy, aperture means the effective diameter of the light collecting element. Whether is a lens or a mirror. No relation to the F from photo. Also, in astronomy, F, or some time F/D, means the ratio between focal length and diameter, in the same way as in photo, with the difference that you can't change the F, because their is no diaphragm.

The 560mm/5,6 is a lens with a 100mm effective diameter, at least in theory. I never saw one in reality. So, the DA 560mm/5.6 must be better in IQ that this spotting scope with his 65mm diameter.
Most any spotting scopes have a built in prism to turn the image right side up and correct left-right when using with eyepieces and does degrade the image slightly. Used mostly for terrestrial daytime. Hunting and Birding.

04-19-2015, 05:31 PM   #20
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QuoteOriginally posted by csa Quote
Nope; the XW eyepieces, which are top of the line are still available. I have 3 of them.

https://astronomics.com/pentax-xw-eyepieces_c80.aspx
Yep. I just bought a Pentax 10mm XW eyepiece. Came in a silver Ricoh label box, too.
04-19-2015, 05:57 PM   #21
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Are there any guides to using a Pentax DSLR with a telescope? As in a simplistic how-to of all the equipment required to mount and use a telescope with the camera? I have an Orion telescope and I have a Pentax DSLR.. would be super to be able to use them together.. even if only looking at the moon or bright stars.
04-21-2015, 02:00 AM   #22
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I want that guide, too!
Anybody, please?

:-)
04-21-2015, 03:09 AM - 1 Like   #23
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QuoteOriginally posted by mee Quote
Are there any guides to using a Pentax DSLR with a telescope? As in a simplistic how-to of all the equipment required to mount and use a telescope with the camera? I have an Orion telescope and I have a Pentax DSLR.. would be super to be able to use them together.. even if only looking at the moon or bright stars.
T-mount nosepiece would be the simplest option - for a DSLR 2-inch one would be better - like this one:
FLO 2-inch T mount camera adapter - First Light Optics
Of course you would also need a K-to-T mount adapter, then you can just mount your camera instead of the eyepiece. That simple.
Without tracking it will be just for the Moon and the brightest planets, like Jupiter. Also Sun, with proper safety filters of course!

04-21-2015, 03:54 AM - 1 Like   #24
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It's more complicated to explain, than to mount a camera to a telescope. But I will try to present you the basic tools you need to connect the camera. I will use a German site to show the pieces, cause I know it better, but you can it find almost in any big astronomy store.

First you need an adaptor from the 2'' (or 1,25'') focuser, with a T2 screw. Like this:

http://www.teleskop-express.de/shop/product_info.php/language/en/info/p200_T...l-Adaptor.html

http://www.teleskop-express.de/shop/product_info.php/info/p201_TS-Adaptor-1-...T2-thread.html

This will be inserted in the focuser. In the T2 end of this adapter you will need a T2 to Pentax K adaptor, like this:

http://www.teleskop-express.de/shop/product_info.php/info/p2759_T2-Adaptor-f...R-Cameras.html

And that's the basic. Of course, this is the most simple thing, but you can start to make some pictures. Regarding the telescope you use, you must take care at the back focus distance. For example, many Newtonian telescopes can't reach focus with a camera, if their are not made special for astrophoto, because their back focus is to short. And you must have more than 55m from the focal point to the face of the focuser when is fully retracted. And, as I said, some Newtonians are made only for visual use and has a back focus of about 12mm. In this case you must move the primary mirror up in the telescope tube. It's not a very simple job, but is perfectly doable with a little attention. On the opposite, other types of telescopes like SC (Schimdt-Cassegrain), Mak (Maksutov-Cassegrain), or RC (Ritchey-Chretien), has very long back focus, and you might need an extender tube to reach focus.

You must take into account that you might need some other accessories, like correctors, filters wheels and other. And those accessories could also take some space in the back focus.

As you will see, the subject is big, and it needs many pages to explain everything that can come in. So, better take a look at astronomy forums, like Cloudy Nights, or Stargazers Lounge, or others. There are hundreds around the world with lot of informations about the subject.
04-21-2015, 06:28 AM   #25
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Thanks, guys, for the responses. This is why I was suggesting an official how-to guide on the PF main page! ;c ) looks involved!
04-21-2015, 06:59 AM   #26
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Now I see that ''back focus'' make a connection to the term back focus in photography dictionary. Their is no relation between those notions in photography and astronomy. In astronomy, back focus is the distance from the end of the focuser to the focal plane of the telescope, when the focuser is fully retracted, or put at the infinite point, like is the case for SC, Maks, or RC.
04-21-2015, 07:07 AM   #27
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QuoteOriginally posted by JimmyDranox Quote
astronomy forums, like Cloudy Nights
I agree. Anyone interested in astro photographing, or just interest in astronomy, CloudyNights.com is the largest astro site with over 80,000 members to help you with any questions you may have. However, you may be able to get enough information right here, as some of the members have posted.
04-21-2015, 07:16 AM   #28
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QuoteOriginally posted by JimmyDranox Quote
It's more complicated to explain, than to mount a camera to a telescope. But I will try to present you the basic tools you need to connect the camera. I will use a German site to show the pieces, cause I know it better, but you can it find almost in any big astronomy store.

First you need an adaptor from the 2'' (or 1,25'') focuser, with a T2 screw. Like this:

This will be inserted in the focuser. In the T2 end of this adapter you will need a T2 to Pentax K adaptor, like this:
Can the Pentax PF-CA35 T-mount to K-mount adapter/teleconverter be used with mirror scopes, or is it solely for use with spotting scopes like Pentax's PF-80ED and PF-65ED?
04-21-2015, 08:24 AM   #29
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I can't say exactly about this piece, but from my experience, adapters for spotting scopes have a different barrel than 1,25'' or 2'' which are standard for telescopes. What I can see from specifications, is that this adapter is in fact a projection lens. And with 12.5 fix aperture (focal/diameter ratio), and magnification included, I wouldn't recommend it for use with anything other than Pentax spotting scopes.

With the adapter set up I have described before, you will have the native F/D ratio of the telescope, which can be much faster for some of them. And you can modify it with the help of a Barlow lens.

What kind of mirror scope did you have?
04-21-2015, 08:14 PM - 1 Like   #30
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challenging

QuoteOriginally posted by mee Quote
Are there any guides to using a Pentax DSLR with a telescope? As in a simplistic how-to of all the equipment required to mount and use a telescope with the camera? I have an Orion telescope and I have a Pentax DSLR.. would be super to be able to use them together.. even if only looking at the moon or bright stars.
I am investigating this now. Two main forms of photography are possible with any DSLR.

1 is called Prime-Focus photography and means you attach the camera directly to the scope without an eyepiece. This will give you limited magnification (which in some cases is good for nice wide-field views of sky or landscapes), however, the image will be upside-down (in a spotting scope with prism built-in. A simple refractor telescope will have a correct view with camera directly attached)! A pain in the *** to deal with for me anyway.

2 is called Afocal photography and is a form of "digiscoping" where you attach the DSLR directly to the eyepiece already in the scope eyepiece holder. If you use an Amici style diagonal, the image will be right-side-up and left-right correct. But that is using a telescope, not a spotting scope that has a prism built inside of its waterproof body. I don't have to worry because I don't own a spotting scope, only a telescope, so the Amici diagonal works for me. Using with the eyepiece also give you most magnification (and most vibrations and unwanted movement!). I would think a spotting scope has an amici-style prism inside in order to get right-side-up/correct left-right views for the mostly terrestrial views demanded by hunters and birders, but don't quote me.

The Pentax eyepiece I have 20mm XW has a built-in male 43mm thread. The Pentax XF eyepieces do not have a thread on top. Most don't. I attach a simple chinese 42-43 step up ring to the eyepiece thread making it present a male 42mm thread to the camera's T-adapter (female 42mm thread). This is all assumed to be standard filter-sized pitch of 0.75 mm/thread. Some telescope manufacturers make life miserable and use odd-ball threads and pitches just so they can sell you their wildy overpriced adapters. Zeiss uses 44mm. Takahashi uses 36.4mm (.75 pitch) as well as 43mm (1.0mm pitch), Celestron may use 54mm on some telescopes, Vixen uses 60mm, Borg uses 57mm, old Pentax threads are 42mm 1.0mm pitch, etc, etc, etc. Nothing is standardized except that a T-adapter attached to the DSLR camera ALWAYS presents a 42mm female thread on the lens side.

Don't EVER cross-thread two items that have wrong pitch!!!! You will ruin BOTH items by ruining the threads. Most that say "52mm filter threads" have usual 0.75mm pitch used in photography, as an example.

Cloudynights is wonderful but you really need to be careful to ask newbie questions in the correct forum.

Good luck!

Last edited by goldenarrow; 04-24-2015 at 08:45 PM. Reason: clarified the view of Prime Focus with refractor telescope
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