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21
ATM, Optics and DIY Forum / Re: Artficial star distance?
« Last post by risodachest on February 09, 2018, 11:23:54 AM »
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For a star test the incoming wavefront needs to be as flat as possible. This requires the pinhole to be placed at the infinity focal point rather accurately for generating the beam.

It's much better to test your scope using autocollimation. You don't need long hallways and the sensitivity of the test is twice that of the ordinary star test.

Mladen
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Eyepieces Questions & Recommendations / Re: Uh-oh...
« Last post by Stephen Moritz on February 09, 2018, 11:23:06 AM »
My bino pairs include some Tak orthos. It has taken 4 years since buying the binoviewer to get to this line up, there's been a lot of buying and selling along the way. Tried TMB SMC, Brandons, UO and BGO as well. They are all good eyepieces. The Tak orthos are a step up from the run of the mill abbe's, they are close to the ZAO II. They have great coatings and very low scatter and are extremely sharp. I have a thing for good looking field stops, and the Takfield stop is the sharpest of any eyepiece I have used. Certainly way better than the rough UO and BGO stops, and even the ZAO. The build quality and design of the Taks is also a notch above all the other orthos.

If anything, I'm surprised how cheap they are for the overall package you get.
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I just gave myself a one-year astronomy fix by putting down deposits for a JP Astrocraft "Sweet 16" scope as well as a Lockwood 1.1-thick Cer-Vit mirror. The speed will probably be about f/3.7 to allow a very comfortable seated position even at zenith, where the eyepiece will be at ~60". The scope and mirror probably won't be ready until next summer at the earliest, but that does give me time to nail down the details.

I've got two kinda stupid questions, "stupid" in the sense that despite doing research I still haven't come to a concrete conclusion!

1. In terms of determining whether I should put the focuser on the left or right side of the scope (when viewed from the back), this second half on body temperature in this Daniel Mounsey article (as well as his numerous other CN posts) has been very helpful.

I live and observe in Boston. Is there a prevalent (marine layer) nighttime wind direction in Boston? Logan airport seems to report that the wind is NW-ish most of the year but day-to-day I seem to observe a more expected wind from the east at night. For some strange reason, despite being left-eyed, I greatly prefer having the focuser on the left side which would be work well with a wind from the W to NW.

2. I have precious little time to observe nowadays. We're talking less than half an hour, with a hoped-for setup time less than 5 minutes -- including wheeling the scope in and out. I also don't have the bandwidth to set up a scope beforehand: with a growing family I will inevitably forget that I had set up the scope and it will rain overnight and the sun will burn my house down the next day! So not only is cooldown important but high quality views *while* the scope cools down is of utmost importance.

The thin Cer-Vit mirror should hold its figure and cool down rapidly. That leaves the boundary layer to deal with in those precious first few minutes: what’s the latest thought on removing its effect?

FYI: this wondrous thread has been my guide on boundary layer mitigation, but it is from 2005. Daniel Mounsey concluded at the time that it is sufficient to have a single rear fan blowing on the primary as well as a bank of venting fans on the top side of the mirror box to pull the boundary layer off, kitchen hood-style.

At the same time, Mike Lockwood just posted an interesting article on a customer's method of merely "stirring" the boundary layer with four internal fans with zero venting to the outside other than what goes out the top of the scope.

Perhaps the best combination would be a couple "stirring" fans at the bottom of the mirror box, pointed directly at the mirror at very low speed to assist in stirring the boundary layer (mitigating its effect while it exists), plus a bank of fans Daniel Mounsey-style at the top of the box to pull out the (now-stirred) boundary layer? Or is the bank of pull fans sufficient (or even better) by themselves?
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How did you attach the safety line to the mirror and holder?

Did you use the same silicone that you glued the mirror with to bond the safety line to the back of the mirror and holder?

It would seem that if the silicone that held the mirror failed then it would also fail with the safety line.


I did not use the same adhesive, I either used epoxy or cyanoacrylate.

Jon
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Instead of disassembling the EP why not engrave on a filter (clear or light color) and screw on to the bottom of the EP?
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Eyepieces Questions & Recommendations / Re: Edmund 8mm RKE vs Televue 8mm Plossl
« Last post by ndesevtenzio on February 09, 2018, 11:20:11 AM »
The RKE is a modified Kellner and it performs rather well.

People generally feel Plossls and Orthos are better, but I also really enjoy using the RKEs.

And of course the 28mm RKE has gigantic eye relief in a small body and when observing through it the eyepiece appears to disappear.

I was showing someone brand new to astronomy objects all night using some nicer eyepieces. At the end of the night I decided to show him the 28mm RKE. He was like, "woah...that's really cool!". He liked the RKE more than the more expensive eyepieces.

I will say this. They are very good eyepieces which are better than Kellners and could be debated when compared to Orthos and Plossls. Certainly nothing wrong with them. And not too many other eyepieces provide the illusion that the 28mm RKE does. I also find they do a good job for solar observing. One could probably get a full set of them for under $160 or less. Brand new it's probably better to go with a set of Plossls or Orthos other than the 28mm.
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Mounts Questions & Expirience / Re: Polemaster final alignment help
« Last post by Zachary Patterson on February 09, 2018, 11:19:24 AM »
This also happened to me - I bumped up the camera exposure a notch, and it seemed to fix it.  Not sure if that was really the cause though.
I hope the next version of the software is more like the method used in sharpcap 2.9.  So much easier:)
28
Mounts Questions & Expirience / Re: Do I need APCC?
« Last post by Pablo Abreu on February 09, 2018, 11:18:34 AM »
I purchased APCC. Then I uninstalled it from my computer. That should tell you something.

Maybe the software has great functionality, but it also has one of the worst user interfaces I've ever seen. I got tired of flashing windows and error messages. (Reminds me of the scene in Apollo 13 when every light on the panel starts flashing error messages.) Just way, way too complicated. Never could completely figure out the virtual port. Worked OK when it worked but if something went wrong... After spending 30 minutes one evening trying to debug a problem I just uninstalled it and went back the standard A-P Ascom Driver V2 interface.

Maybe some day I'll try again. Not sure.

I run my AP1100 with TSX and SGPro. Works great. What I find really nifty is I plug my phone via SkyWire into the other serial port on the CP3 and use it as a hand controller via Sky Safari V Pro. Allows me to nudge the scope around while standing at the eyepiece, finder scope, or at my computer station.

MJB
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Mounts Questions & Expirience / Re: Friction drives. Potential problems?
« Last post by ciomasbure on February 09, 2018, 11:17:50 AM »
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cool, finally ... what resolution are the encoders on Ra dec, if enough it could be used to do interpolation so you can do unguided imaging ...

/Yves

No, they are not from my understanding. High resolution encoders are an option.
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Years ago, before I knew of CN, I considered getting curved secondary holders because I mistakenly thought that they eliminated diffraction. For DSO observers like me, that hardly ever look at anything bright, curved vanes are not worth the trouble or expense.



The essence of the matter. Your habits and preferences rule this choice too.
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