Initial Test Images

[rjbokleman]

Get well, Chuck.

As an option there are some higher end Bahtinov masks made by Spike-A http://spike-a.com. Instead of the polystyrene type these are aluminum and have 3 nylon thumbscrews to attach to your dew shield or on the outside edge of an SCT.

[Chuck]

Thanks Ron. The mask I purchased was the plastic one from Farpoint. Not sure when I'll get to try it out, though hopefully soon. Are you using the one from Farpoint? If so, are you having problems with it and why you suggested the one from Spike-A?

----- Chuck

[rjbokleman]

I have an FP-410 for the C8. This one was intended for use with the Hyperstar option, but works just fine. Place it on top of the corrector plate and it easily removes.

I did, however, order two previous units for my 3-4" refractors from Spike-A. The difference being the manner in which they attach to the scope and the material they're manufactured out of. As I said, the Spike-A units are higher end, made from anodized aluminum and attach with thumbscrews on the dew shield.

The Farpoint ones are lighter and less money and don't suffer from sharp edges like the Spike-A ones do. It's really a a personal preference / $ thing.

In my case, I like the Spike-A ones for my refractors and the Farpoint one for the C8. However, I did just order a 10" Spike-A for the C8 to give it a try.

[Pete]

I'm usually out at twilight and seeing is so turbulent that all focusing technologies are a rough guess at best. My tube requires refocusing once it's fully dark and subsequently every 5 or 6°F drop in temperature. My homemade mask isn't as helpful as a 3" diameter aperture mask for focusing the camera at twilight, but the resulting f/30 or so rig isn't that good either.

Pete

[Chuck]

@ Ron: Thanks for the info. I'll be interested to hear how the Spike-A mask works out for you on the C8.

@ Pete: Once I finally get a chance to try out the Bahtinov mask on my rig, I'll definitely be rechecking focus with it over time to see how it changes.

---- Chuck

[rjbokleman]

One of the beautiful things about running Sequence Generator Pro (SGP) is that it provides an Image History alongside the Histogram.

Image History, provides constant feedback on each image taken with Star Count and Focus. When you start to see the Star Count drop and the Focus (HFR) increase it's time for a refocus.

http://www.mainsequencesoftware.com/Con ... tory1.html

Each scope is different with respect to temperature changes and each night different, of course, due to the actual weather. My refractors between 330mm-765mm hold focus very well over wide temperature ranges, but I attribute that mostly to their shorter focal lengths. When at 900mm temperature affects are more noticiable...especially during the winter when it can start out at 40 and drop to near zero.

The C8 @ 1422mm holds fairly well over two hours and a 10-15 degree drop, but I do have to refocus slightly. With SGP, it's not too big of a deal:

Pause the sequence underway.
Pull off the dew heater.
Insert the Bahtinov mask.
Slew to a bright star, nearest the target.
Refocus.
Slew back to original target, center, and check camera rotation.
Dew heater back on.
Resume sequence.

[Chuck]

Hi Ron:

Just curious if you have had a chance to try the Spike-A for your C8 yet and if so, how it compares to the Farpoint mask? Myself, I've been out of the AP loop for almost two months now. I'm finally getting back on track and hope to try some more testing soon. Good luck at Plainfield and hope you get to finish up the Crescent Nebula. Look forward to seeing your final result. --- Chuck

[rjbokleman]

Chuck,

Like most things, there are pros and cons to both.

The Farpoint unit (Styrene) is the one with the cutout for Hyperstar option on the C8 EdgeHD. It sits down inside nearly on top of the corrector plate. So you just drop it in, no screws to mess with, but taking it out again without touching the corrector plate must be done delicately. Its very light and flexible, so if you drop it or step on it...no issues. Knowing which way to turn your focus knob can be a challenge if you don't put it in with the same pattern each time and it tends to not center exactly if your scope is pointed downward a bit...it just hangs on the center mirror.

The Spike-A unit (Aluminum/10") fits over the end of the C8 EdgeHD and has nylon screws to hold it into place. Taking it on/off is easy as is orienting it the same way each time so that you know exactly which way to turn your focus knob from the resulting star pattern. It has rather sharp edges, and if you drop it is going to get marred up a bit (patio/concrete pad) unless you're on grass. If you step on it...it might bend and/or break off one of the nylon screw tabs on the edge...though it seems rather rugged and is speculation on my part. It gets COLD and thus seems to attract a bit more dew buildup than the Farpoint.

As far as quality of the star projected...they seem the same. I was expecting the Spike-A to give me a slightly better focus due to its sharper edges, but it would be really, really hard to measure any difference between them. If there is any...its a pixel or two in clarity.

I like them both and wouldn't do without either one. If I were get the Hyperstar for the C8 later...then only the Farpoint would work as the Spike-A just wouldn't reach back that far to attach to the scope.

[Chuck]

Ron,

Thanks for the info. I'll be sure to be careful when I finally try the Farpoint mask on my Meade 8" SCT. I am anxious to see how using the mask affects the focus in imaging on my system. Take Care.

---- Chuck