Posts Made By: John Biretta

July 5, 2013 07:14 PM Forum: Digital SLR AstroPhotography

Cheap and simple

Posted By John Biretta

If you have a computer you can place near the telescope, this would be one possible way to do it:
http://www.telescope.com/Orion-StarShoot-USB-Eyepiece-Camera-II/p/102083.uts?keyword=camera

The computer will need a USB port, but most computers made in the last 10 years or so will have it.
I am not sure this camera will work with Apple computers.

If the telescope accepts 1.25" eyepieces, you should be all set. If it takes 0.965" eyepieces,
you would need an adapter like this:
http://www.telescope.com/catalog/search.cmd?form_state=searchForm&keyword=adapter+0.965

July 15, 2013 04:39 AM Forum: A Day in the Life of the Administrator

The AstroMart FORUMS - What I like and HATE!

Posted By John Biretta

OK, what am I doing wrong.... Starting in the last few days the ad images all display in a 2:1 ratio of width:height. Hence, nearly all of the images are cut off at the top and bottom. The only way I've figured out to see the entire images is to save them to disk, and then display them from disk, which is a pain. Is there some way to preserve the original aspect ratio of the images? I am getting this behavior with both IE8 and Google Chrome 28. Thanks! - John B.

July 19, 2013 04:03 PM Forum: Home Observatories

Tool shed

Posted By John Biretta

Just google "rubbermaid shed observatory" and you'll find lots.

http://thadlabs.com/MAPUG/AstroDesigns/MAPUG/ShedObsry.htm

http://www.marsastro.org/presentations/MARS_Home-Observatory.pdf

I also recall seeing pics of one after being destroyed in a wind storm. Bits of plastic all over a hillside. Pretty much nothing left. See if I can recall where it was....

September 19, 2013 02:40 AM Forum: Mounts

Attaching C-11 to mount by yourself

Posted By John Biretta

As others have commented, a tip-in rather than a slide-in dovetail saddle helps. For my C14 I use this process: I place a tall table next to the mount (like a camping table with home-made extensions on the legs) -- it needs to be about the same height as the pier or tripod. I put the C14 on the table, then turn it so it is pointed nose-down, slide it over to the mount, set the mount so the Declination axis is horizontal, and then attach the C14 to the dovetail saddle on the mount. Then I put the counter-weights on the mount and let the mount do the heavy lifting. Once the mount has lifted the scope off the table, I'll move the table away.

October 2, 2013 08:26 PM Forum: Refractors

Under/over correction and width of air space

Posted By John Biretta

A typical Fraunhofer achromat (like you are describing) will go under-corrected if the air space is too wide. Typically these are designed for 0.1 mm airspace. That said, the spherical correction for an F/16 lens changes very slowly as the airspace changes. If the spherical correction is very far off, re-spacing is probably not going to fix it.

Robert Apruzese said:

If an air spaced objective has too wide an air space, will this contribute to under correction or over correction? Same question if the air space if too narrow. Final question: For a 60mm f/16 objective, does anyone have an educated guess as to what the optimum air space gap would be ? Thanks in advance.

October 3, 2013 03:54 PM Forum: Equipment Talk

Sidereal Tracking on a 1980's C8

Posted By John Biretta

The difference between solar and sideral rate is very small. I doubt you would notice it unless doing long-exposure photography. You can probably just connect to household AC power or a standard inverter output (12v DC to 120v AC converter widely available) without any noticable issues.

Accutrack controllers sometimes show up on Astromart. JMI MotoTrack units will do the same job. Don Rothman sells a lot of old parts -- google "astro parts outlet" -- maybe he can help.

October 31, 2013 08:07 PM Forum: Refractors

Move from catadioptric to refractor

Posted By John Biretta

The Sky-Watcher 120mm ED doublet APOs have generally gotten good reviews for optical performance. Prices are around your budget. Might have a look at those:

Ads:
http://www.celestron.com/astronomy/celestron-sky-watcher-pro-120ed-apo-with-cgem-mount.html
http://handsonoptics.com/index.php?main_page=product_info&cPath=1_171&products_id=2324
http://www.astromart.com/classifieds/details.asp?classified_id=835663

Reviews:
http://www.cloudynights.com/item.php?item_id=2742
http://scopeviews.co.uk/SW120ED.htm
http://stargazerslounge.com/topic/104445-the-skywatcher-120ed-review/
http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/3678502/Main/3675349

The Orion EON 120 is a similar scope. I don't see them listed new anymore, but
there are probably used ones around.

A completely different scheme woud be to stay with an 8" SCT, but on a German
Equatorial Mount. That might involve less massive pieces to assemble and set up:

http://www.celestron.com/astronomy/celestron-advancedvx-8-inch-schmidt-cassegrain.html

November 24, 2013 08:09 PM Forum: Digital SLR AstroPhotography

Can 20Da do itself stacking and dark frames and ho

Posted By John Biretta

As far as I am aware, the 20Da cannot do internal stacking of frames. All it can do is take one frame, and then take one dark frame, and then internally subtract it via the "noise reduction" feature. But this is not a very efficient way to use the camera.
It would be more efficient to take dark frames at the start or end of the evening (though they are somewhat sensitive to the camera temperature).

You can automatically take data and dark frames using the electronic remote control cable. It can be programmed to take some number of frames automatically. But you need to stack and subtract them outside the camera.

Stacking and dark frame subtraction is very easy on a computer using a program like "deepskystacker." It is a free program. You tell it which images are the target, which are the darks, etc., and it does most of the work for you.

December 17, 2013 10:23 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 10:27 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?