Posts Made By: Michael Minnhaar

Damage is possible, but it takes more than just the t-mount adapter on its own:
There are a couple of electrical contact pins in the lens mount, which the t-mount ring itself will not touch. Just put the t-mount ring on its own on the body and see yourself.
*But* if the lens/scope that threads into the t-mount has a metallic front surface *and* it protrudes far enough towards the camera it can sort some supply voltage pins there. Its usually "just" blowing a fuse inside the camera and its dead right away.
If you can do electrical measurements, I can post here how to check for this in more detail.

Michael

I got a EQ-6 a year ago for imaging and I'm happy with it, too. 15" PE, very smooth, only thing I had ever to fiddle with was setting the DEC backlash compensation right to get perfect autoguiding.
Michael

The surplus electronics shop near me definitely has lots of large diameter shrink tubeing in their showroom.
Give them a call, as most of their stuff is not on the webpage.

www.surplusgizmos.com

Michael

Here is what works for me, all used prices on Amart unless noted.

$800 Vixen R200SS + CC
$600 EQ-6 or HEQ-5 mount
$500 Canon Rebel XT
$12 T-ring, new
$35 Meade 70mm cheapo achro
$25 Webcam TOUCAM or QUICKCAM, ebay
$18 Orion 90mm rings, new
$9 for a 1/4" tap and 6 nylon screws to complete DIY guidescope rings
$20 shoestring guideing interface

If you consider the DSLR as not astro specific, its close enough to your budget.

Goto is maybe worth $200-300, but not the amounts it costs on a new losmandy.
And its worth less if you are serious about astronomy, since once you're a bit more famliliar with things and you go for smaller or fainter stuff, its less helpfull.
Value for Astrophotography = zero.

Michael

For Widefield EP's, most of which have significant distortion, the simple assumption that TFOV=FOV/magnification can be quite bit off. When calculated useing the real fieldstop diameter the numbers are:
35mm pan = 38.7mm fieldstop = 1.75deg TFOV
32mm WF = 34.6mm fieldstop = 1.53deg TFOV
For the ortho the simple formula FOV/mag is likely very close, as the name orthoscopic just means it has no field distortion, so its some 1.2deg TFOV at best.
Which puts the ortho not that much behind the widefield.
On the question with the double cluster - its 1.5 degrees across both parts.

Michael
P.S. I use a GSO 42mm superview as a finder - 46mm fieldstop !

Yes, they are perfectly interchangeable and both are the same as a EQ-5 mount type dovetail.

Michael

There is no "formula" as the location of the focal plane is determined not only by focal length and eyepiece type/construction:
E.g. take they very same eyepiece and mount it in a longer case, so that all lenses are 1/2" further away from the EP barrel and its no more parfocal with its unmodified sibling ...

For you that means: Every eyepiece requires a different focuser travel, which can be measured for every EP (its called the focal plane location), but I can't be predicted from other EP data.
Once you have this location, any two EP with the same focal plane location are parfocal. IMO only Televue specified this number for their EP.

Michael

Here is an example how to measure FPloc, the location of the focal plane of an EP, which I use in my spreadsheet. This might also help to understand how to use this number to predict how much focuser travel any other EP in the database will need.

First set up your scope, so that you can focus it on something. Anything will do, so this can be done in daylight and with a very close in object. Use a diagonal as needed.
Tape a metric scale to the OTA of your scope, so you can read the location of a mark on the drawtube (moveing part of the focuser) with it. In my example I stick a post-it note on the diagonal, since this moves just like the drawtube.
Now we calibrate the setup - by useing an EP for which FPloc is know. E.g for any Televue EP, FPloc is listed as Dimension F at http://www.televue.com/engine/page.asp?ID=144.

Now, after focusing with this known eyepiece, adjust the mark to point to the correct FPloc for this EP. In my example, the TV 3-6mm zoom has FPloc=+6.2mm, so I point the mark to point 6mm outward of the red 10cm mark, which I use as my reference.
Then exchange the EP and re-focus. The mark now points to the FPloc of the new EP. Instead of many words I just like to refer to the two insets in the attached picture giving examples for different EP with different FPloc.
One final word of caution: When changeing from 2in to 1.25in EP an adapter might be used that extends a bit outside of the 2" barrel. This has to be accounted for by moveing the mark by the amount of this extension. Or better recalibrate the setup with a known EP of the same barrel size.

What you describe is exactly what the reticle of a polar finder scope does for you. Just, rather than calulateing the position angle from date and time you just look at the position of other known constellations around polaris.
The red cross denotes the location of the true celestial north pole, about 3/4 degree away from polaris in direction of Kochab, the brightest star in the little dipper. The end of the big dippers handle works as well to determine that direction.

Michael