From memory there is a paper by Couder on the subject but pass on where and when I read it. Seems that anything affects the light in the central spot. It went...
12410
Tony Gondola
acgna
Jul 1, 2008 2:45 pm
John, Here's a link to a short paper by Harvey and Ftaclas, one of the best I've seen on te subject: ...
12411
zway2bisfancyfree
zway2bisfanc...
Jul 1, 2008 3:25 pm
... Hi Phil, It kinda depends on the size and weight of the DOB, but what I do is use one of those target shaped bubble levels to level my groundboard. I am...
12412
a.johnw
Jul 1, 2008 3:40 pm
I'm always a bit queasy about papers like that Tony. Shading must be one aspect but if the diffraction spikes can be seen the light has to come from some...
12413
Tony Gondola
acgna
Jul 1, 2008 3:50 pm
The main impression that I took from the paper is that vane area and shape is what really matters. Taking everything they state at face value the best choice...
12414
Dale Eason
atmpob
Jul 1, 2008 4:24 pm
Thanks to Tony for posting that paper. The other day I was trying to use OpenFringe to predict the performance of the MMT we talked about recently. To test...
12415
jacques savard
suppjos
Jul 1, 2008 5:00 pm
at the time a made my curve spider I do not know howto only ear soembody speaking about and my version is a bit new I only made a circle of 12 inch ( my...
12416
jacques savard
suppjos
Jul 1, 2008 5:10 pm
Addition but may main solution is this http://bhs.broo.k12.wv.us/homepage/alumni/dstevick/double.htm a Jose Sasian solution ...
12417
Nils Olof Carlin
nilsolofcarlin
Jul 1, 2008 5:14 pm
In ATMJ #11 (reprinted in WillBell's tbe best of ATMJ vol 1, p.385, if anyone has it) is an article by Suiter and Zmek, "A Dialogue on Spider Diffraction"...
12418
Stephen Koehler
steve_koehler
Jul 1, 2008 6:53 pm
... It turns off I wasn't off by a factor of two, so my corrected diagrams are wrong. To interpret them correctly, consider them to be from an 8" scope...
12419
Mark Cowan
toolontop
Jul 1, 2008 7:39 pm
A great advantage of extremely thin vanes or wires, and unachievable with curved vanes due to physical limits, is that as the vanes are made thinner the...
12420
Stephen Koehler
steve_koehler
Jul 1, 2008 8:07 pm
Mark, ... I could probably push it to .001 of the primary diameter. The R implementation of FFT isn't constrained to powers of 2 in size, but the upper limit...
12421
Tony Gondola
acgna
Jul 1, 2008 8:17 pm
That's right, the energy is less and it's spread over a much larger area making it's impact on extended object contrast very low indeed. I've wanted to do a...
12422
Tony Gondola
acgna
Jul 1, 2008 8:22 pm
Steve, You should be able to find what you need here: http://apollo.sese.asu.edu/ Tony BigEye Optics ... From: "Stephen Koehler" <s.c.koehler@...> To:...
12423
Mick D
liquidgold999
Jul 1, 2008 9:38 pm
Hi Guys I I feel a bit reluctant to join in this discussion mainly because all you guys seem to really know your stuff, but there is one thing that i would...
12424
Tony Gondola
acgna
Jul 1, 2008 10:04 pm
I can think of a couple of reasons. First is cost, you can't use just any old bit of glass for this. It has to be optically clear and uniform and have a good...
12425
Stephen Koehler
steve_koehler
Jul 1, 2008 10:05 pm
Mick, ... Here are some reasons I can think of: pros: - gets rid of diffraction spikes from the spider - perhaps keeps primary cleaner cons: - expensive to...
12426
Al Germaine
trulyyours05
Jul 1, 2008 10:34 pm
Mark, Thinner is better... maybe not. You not only have to make sure the wires are strong enough to hold the load, they have to be strong enough to make...
12427
Al Germaine
trulyyours05
Jul 1, 2008 10:43 pm
Mark, That is not at all a dumb question. This is sometimes done. A glass plate holding a secondary is called an optical window. An additional benefit is that...
12428
Mick D
liquidgold999
Jul 1, 2008 11:13 pm
So in short it causes more problems than it solves and thats without mentioning the cost. Well i just had to ask. Cheers guys Mick ... From: Al Germaine To:...
12429
Al Germaine
trulyyours05
Jul 2, 2008 12:09 am
Not that it causes more problems. It's that there's a trade off. Some people use them. Al ... - how measured? ... will ... an 8" ... simulation, ... have a...
12430
Al Germaine
trulyyours05
Jul 2, 2008 12:26 am
I think I should mention that for larger scopes, wire makes less sense because the load goes up with the cube of the size, so the wire diameter outpaces the...
12431
a.johnw
Jul 2, 2008 9:10 am
The main thing is cost. It doesn't have to be flat but the thickness needs to be very even and it needs to be made of a decent optical glass. The surface can...
12432
jacques savard
suppjos
Jul 2, 2008 12:57 pm
ok ((((The major problem may be to get the window coated))) and for a 24 inch size the price jack 47'N 71'W...
12433
Tony Gondola
acgna
Jul 2, 2008 2:59 pm
Getting IR coating done can be a big issue. A lot of companies will try to charge you well over $1000 for something like that. You have to hunt around and find...
12434
Tony Gondola
acgna
Jul 2, 2008 3:07 pm
lol....geeezzz....read IR as AR please. Tony ... From: "Tony Gondola" <acgna@...> To: <atm_free@yahoogroups.com> Sent: Wednesday, July 02, 2008 8:59 AM...
12435
Ulhas Deshpande
dulhas2001
Jul 2, 2008 4:24 pm
Hello I was running the excellent simulation program 'Diffract' to compare the shadows I see on my 158 mm f 4.5 mirror,when a doubt arose. In diffract which...
12436
Dale Eason
atmpob
Jul 2, 2008 6:12 pm
I don't know but here is how to know. When the knife is inside the ROC off all zones all shadows are on the same side as the knife. Dale Eason...
12437
Mark Cowan
toolontop
Jul 2, 2008 7:06 pm
Right to left, positive to negative - as in the help file: "Y is positive to the right, looking toward the mirror." Best, Mark...
12438
a.johnw
Jul 2, 2008 7:37 pm
I don't know if any one on here knows how AR was done some time ago but I would love to know too. I've tried searching several times. It seems it can be done...
