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Posts Made By: John Biretta

December 17, 2013 02:23 PM Forum: AstroMart FAQ

Would you buy from someone who doesn't post a pict

Posted By John Biretta

Probably the reputation of the seller, and the ability to have good communications with the seller, are more important than pictures. Pictures certainly help, but they are only one of many factors. If other factors are good, then I'm OK dealing. A couple emails or a 5 minute phone chat can often give you a better sense of things than some pictures.

I can certainly understand that some days you can't find a working battery for the camera, or all the memory cards have disappeared, or the charger got left somewhere 3 flights ago, etc. Or its a lot of trouble / delay / expense to get the film(!) processed and scanned. Not everyone has an iPhone or the latest Samsung Galaxy....

Pictures can also be misleading. I've certainly bought some stuff where the pictures look beautiful. But then you get the item and realize they were done in a very clever way so every gash, dent, paint scrape, etc., is out of view. I also know a few folks that take all their pictures from three feet away and usually out-of-focus -- OK it looks like an eyepiece -- but its not a very helpful picture. There also well-known cases of pure fraud on other sites where the photos are great, except they were copied from some other website, and there is no such item for sale at all. So while I would consider pictures helpful, they don't necessarily prove anything.

December 17, 2013 02:27 PM Forum: Antique/Classic/Vintage Optical Instruments

No Baby Blues with this Brandon!

Posted By John Biretta

Beautiful! Who did the glass in these -- was it AP?

May 13, 2014 10:39 AM Forum: Binoviewers

Binoviewers vs. binoscopes

Posted By John Biretta

For "grab and go" something like a TV85 + bino will be a smaller and lighter package.

If you like to view at high power for planets and moon, the TV85, which has an APO (apochromatic) lens, will be sharper. On the other hand, if you plan to do a lot of low-power viewing, the bino-scope (Vixen BT81) will give brighter images (it collects about twice as much total light vs. TV85). So it depends a bit on what you like to look at.

Another difference is that the binoviewer can be used with a star diagonal, and hence give right-angle viewing. This will make viewing at the zenith easier. Many bino-scopes (like the Vixen) give 45 degree viewing, so looking overhead is a bit awkward without some specialize mounting.

May 14, 2014 07:06 AM Forum: Beginning Astronomy?

TASCO 7TE

Posted By John Biretta

Hi Stewart,

I'm not an expert on the 7TE, but might be able to help a little. Japanese eyepieces from that era had an outer diameter of 0.965 inch which sounds a lot like the "just under 1 inch" you mention. Do your eyepieces have 0.965 inch or 1.25 inch outer diameter? Just wondered if this is part of the problem.

Yes, the "Barlow 2x multiplier" is just an accessory that is used part of the time. Maybe not often in that scope.

If you have 0.965 inch eyepieces, and simply need a holder for them, you could try this for a quick fix: Somewhere there you should have a "diagonal prism" which is part 7 in the manual. I was looking at the manual in this ad:
http://www.astromart.com/classifieds/printerdetails.asp?classified_id=754613
You could wrap a some turns of masking tape around the chrome plated 0.965 inch end of the diagonal prism, and then sort of "thread" that into the end of the 1.15 inch focusing tube (part 19 in the manual). If you get the right amount of tape on the diagonal prism, it will sort of catch in the threads inside the focusing tube and hold securely. I've done this on some other scopes from that era that were missing the same part. Then you can put your 0.965 inch eyepieces into the diagonal prism, and observe normally.

You might also check whether part 20 might be there somewhere, but threaded into something else. For example, it might be threaded into part 5 the "erecting prism."

I think that part will be hard to find, but someone probably has one in their junk box somewhere. Someone more familiar with that scope might be able to suggest a modern replacement part. Perhaps Vixen or Borg has a similar part that will fit. You might also check with Don Rothman at
http://astronomy-mall.com/astro.parts.outlet/

- John B.

September 7, 2014 06:55 AM Forum: Equipment Talk

Restoration/upgrade from MEADE MTS-SC8

Posted By John Biretta

I'd start by looking at the coatings on the primary and secondary mirror as best you can without taking it apart. If the coatings have black spots or are missing, then you are looking at a huge project, and not worth it. Dust, light haze, or thin water spots are OK, and would probably wash off.

After that, I'd take it outside at night and see if the optics are OK. Let it cool down for a couple hours outside, and then do a star test -- look at a bright star at high power. Maybe it will need to be collimated. If you can attain images that are very similar on both sides of focus, then the optics are probably OK. If the images are very different on either side of focus -- different halos, or elongated in different directions, then it is probably bad and not worth the effort to fix. Dust and water spots will not have much effect on this test; maybe test it before doing any optical cleaning.

Theres lots of advice available on the web for cleaning optics, so I won't go into that. If the outer surface of the corrector is very dirty, you might clean that first. Hopefully the inside surfaces aren't too bad, and you can try the scope for a while before working on the internal surfaces.

Maybe do some side-by-side test with the 12" you already have. How do they compare? Does the 12" leave the 8" in the dust? Do planets and the moon look better in the 8"? Do you really see yourself using the 8"? Would you time be better spent making the 12" more transportable / usable?

It could be a fun project to clean and restore if the optics are OK, and if you have a lot of spare time. The views would need to be very good to justify the effort. It might also be an educational experience in taking things apart, cleaning, restoration, etc., without much monetary loss if it goes badly.

I think upgrading the mount with GoTo will be a huge project, and probably not worth the effort. The parts alone will probably cost more than just buying a second-hand Chinese-sourced GoTo mount.

If its not good or you don't want it, I would not throw it away, but rather might offer it "for parts" on Astromart or something like that. Shipping the entire scope to a buyer will much more than the $20 you have in it; maybe a local sale would be better.

September 25, 2014 09:37 PM Forum: Refractors

AstroTech 65 Quadruplet Refractor

Posted By John Biretta

Manuel Lois said:

Hello I am new to the forum and new in astronomy. I recently acquired the now discontinued Astro Tech 65 MM Quadruplet refractor
have a few questions
What kind of focuser mask and solar filter can I use for it?
I noticed that the information says that barlows and long eye pieces cannot be used. I am wondering if there is an adaptor/attachment so they can be used.
I have a 2" star diagonal and t adapter for a Nikon D 7000 however I noticed that the telescope has no thread to be able to use these accessories. Any suggestions on how to go about them? or I must buy equipment for the Astro tech specifically and if so what I should get so I can use my nikon for astrophotography.
Thanks for your help

I have not used this scope, but I can try to give you some basic advice. This scope has a lens in the back of the scope, very near to where you put the eyepiece. So you do not want to put anything long into the back of the scope (long Barlow or eyepiece), or it will hit the lens. An adapter will probably not work. There are short Barlow-type lenses you can try -- you might try the TeleVue PowerMate lenses. They work like a barlow, but do not stick into the scope very far. There are other brands with similar lenses.
http://www.televue.com/engine/TV3b_page.asp?id=53
http://www.telescope.com/Accessories/Barlow-Lenses/Orion-High-Power-125-3x-4-Element-Barlow-Lens/pc/-1/c/3/sc/41/p/101910.uts

For the camera, you want to get a 2" camera adapter. One end will slide into the scope, and the other end has a T-thread and will thread into the "T adapter" you already have. It does not need to be Astro-Tech.
http://www.telescope.com/Astrophotography/Camera-Adapters-T-Rings/Orion-2-Zero-Profile-Prime-Focus-Camera-Adapter/pc/-1/c/4/sc/62/p/102119.uts

June 19, 2015 08:25 AM Forum: Mounts

Question about Vixen SP-DX mount latitude adjustme

Posted By John Biretta

Yes my Vixen SP-DX will adjust up to 75 degrees latitude. It can move all the way to 90 degrees, but latitude lock screw does not engage past about 75 degrees. Cheers.

July 22, 2015 03:43 PM Forum: ASTRONOMY

Collimation Meade SCT 12" issue

Posted By John Biretta

What eyepiece(s) are you testing with? You are saying that when you look in the eyepiece, only the center of the field of view is sharp? I don't think a reversed corrector plate would do this.

September 3, 2015 03:43 PM Forum: Antique/Classic/Vintage Optical Instruments

Unitron Black Paint

Posted By John Biretta

There is some info here:
http://www.cloudynights.com/topic/453088-5-craft-unitron-510-restore-turk/page-3

The factory black "paint" on some parts is very thickly applied over a rather inferior metal casting. I'd advise against striping down to bare metal, if you can avoid it. It may be a lot of work to get from bare / pitted / rough metal back to a nice smooth Unitron finish.

November 3, 2015 10:07 PM Forum: Equipment Talk

Obsession 18" f/4.2 UC Question

Posted By John Biretta

I once owned one. Collimation was pretty stable through the night. There was one collimation issue I noticed. The focuser was mounted on the upper ring between two of the support trusses. The ring flexed a little bit between viewing at low and high elevations, so the focuser and hence collimation would shift a tiny bit. But if you collimated at say 20 degrees from the zenith, and observed within say 40 degrees of the zenith, it wasn't too bad. I think a stiffer upper ring would help -- a carbon fiber upper ring would be nice but also very expensive. One could also add some thin extra trusses at the focuser to give the upper ring more support there -- maybe run the thin trusses to the normal truss poles.