Posts Made By: Greg Bradley

You could post this question on the Tak uncensored group but it has come up before.

I think the general idea is to not expose the lens to sudden extreme shifts of temperature. I personally doubt a cooler vent is at the order of magnitude of temperature difference that would cause optics to crack. But leaving a scope in the sun in a car in summer may not be smart or having it outside when it is really hot and then putting it in front of a vent may not be good practice.

The only data I have is if the lens is heated and put into cold water it will shatter. How hot the lens has to be and how cold the water has to be I don't know. Treat it like a fragile crystal glass cup. You wouldn't rinse that in cold water after it held hot liquid. Same deal. My opinion only.

Greg.

Sensational!

Wow, your new scope is a winner.

Fabulous image.

Greg.

Hey, that's quite nice Ivan. I like the colours.

Greg.

That is an interesting area.

You don't seem to have any coma at all. Are you using a field flattener or corrector or is the scope very well corrected?

Greg.

Man, that is a beauty. Well done.

Greg.

Boy you nailed that one! Awesome shot from an awesome scope.
One minor point you could probably salvage more of the bright centre from your data. Try reprocessing it and making sure the background brightness in CCDsoft or whatever you are using allows a large enough dynamic range to keep that centre intact then stretch it to bring out the detail.

Best,

Greg.

Hi Louie,

Good to see you back. Nice shot overall. It seems a little soft for some reason. Was your focus slightly off or was the stacking a bit off?

One thing I am finding with the one shot colour and I am assuming here it is the same for the SXV is that because of the Bayer matrix you can't rotate your images when aligning them or you can't extract the colours. So that means (if I have this right) that polar alignment becomes more critical. Even if you are autoguiding if your polar alignment is off you will get slight rotation between images. This seems to be enough to make it extremely hard to get the colour out and you'll have no choice but to align the images horizontally and vertical but not rotationally. Or you could convert to colour and align and stack the images using something like Images Plus in which case it is not a problem at all ( I think). But it would require a different approach and workflow.

So, if you then align the images and they have a slight rotation to them one to the next the resulting combined image could look a bit soft like that. In experimenting with a M20 shot similar to yours and the polar aligment was off a little bit that was what I found out. Also reading the Sbig application notes on how to process one shot colour brings up this point about the differences with one shot colour.

Do I have that right? This is new to me.

The WO105 is that the TMB lens? Also check the collimation. I had a WO 80mm triplet fluorite and it had coma off axis because the focuser was out of collimation with the lens. I had to fix it with a metal packer which worked. The lens should be one of the best on the planet.

Another recommendation from Sbig and it probably holds true for your SXV is best results come from longer exposures. Try 3 x 30 mins rather than 9 x 10mins. I assume that is because to get the signal to noise ratio on the same level as the mono you need to shoot approx 3-4 times longer due to the Bayer filter matrix on the chip.

The good news of course is you don't need a filter wheel, you don't need to refocus between filters and the colours as in balance rather than working out what the balance is for the tricolour images (its just time saving).

Have you found any advantage to splitting the image into 4 channels and then combining versus simply doing a Bayer convert on the final combined image? I haven't seen an adavantage yet in my limited testing but interested to know what your experience is.

These one shot colour cameras I think have unfairly been given a bad rap in the past. I quite like mine so far. I can directly compare its performance to a mono ST2000XM and I don't see much difference so far and it is a lot more convenient. The above seems to be the main consideration in handling these cameras. Otherwise they seem much the same.

Best,

Greg.

Wow, fantastic image for 4 months experience. You are obviously a bright guy.

My only comments are: 1. frame the shot when doing your focusing. Use the move telescope buttons in your software (I use CCDSoft)so the object is framed exactly as you would like it to be. Also if you frame it well, then at a later night if you want to add more epxosures you can open the earlier shot and compare it to the focus downloads and adjust the framing using the software move buttons to line it up exactly the same which will make combining them later much easier.
2. I was told by Sbig the best results come from 30minute exposures. Go for 3 x 30 minute exposures was what I was told. That may be hard at F12 as your polar alignment and tracking will have to be very good.19 minutes is not enough for a relatively dim object like M27.
4. Take flats and use them as they will help bring out more detail in nebs.
5. Of course shooting at F12 is tough as it is so slow and it is hard on your tracking. Ideally a larger scope would make your job easier there but you've got to work with what gear you have. The SV80s will do stunning wide field shots and I found the image scale is very pleasant with the ST2000XM. I think you will find it easier to do and get very pleasing images from brighter objects that you can shoot at F4.8 with the Televue .8 flattener/reducer for TV85 that suits that scope and camera perfectly.
With that you would have one of the fastest, sharpest and easy to use imaging combos around! But of course, M27 would look very small with that setup. So large nebulas would make a good target for that setup.

Hope this is of some use.

Best,

Greg.

Hi Tom,

That's a great image of an unusual object. I think it came out really well.

Greg.

Hi Louie,

Basically it is very nice. I think though it needs much longer exposures.

I have been told by Sbig that for their one shot colour cameras it is best to have longer exposures like 3 x 30 minutes. It makes sense as the chip has the RGGB filter over it so each exposure kind of has to be 4X the length of a mono camera to get a similar result. You also have to get past the read noise of the electronics which in your camera's case is probably very low but still there.

Why don't you make sure your mount is well drift aligned and then try a 15 or 30 minute exposure and see if that is better than a stack of shorter images?

Best,

Greg.