ONIKKINEN

It would definitely not cost billions to send a repair crew since little new tech would be required. Maybe a modified SpaceX dragon with a radiation shielded habitation module in tow would be enough. Although that's not the NASA way, the true NASA way is to spend as much money as possible and develop everything from scratch, even if alternatives exist so it could very well be billions in that case.

9 hours ago, Maideneer said:

I read somewhere that there is no chance to ever do repairs to the unit once launched.  Can someone smarter than me please explain why that is?

9 hours ago, johninderby said:

Simply too far away as it will be at the L2 point unlike Hubble that’s in a low orbit near the earth.

https://www.nasa.gov/topics/universe/features/webb-l2.html

It is a bit  far away, but i wouldn't call it impossible to send a crew there. From an engineering point of view the spacecraft going there and back in a timely manner needs a fair bit of delta V but not a crazy amount. Somewhere around the range of going to Lunar orbit and back perhaps, and a lot less if the most efficient route is taken (one that JWST takes, which takes weeks). Definitely not an amount that current rockets wouldn't be capable of. Being so far from Earth will mean that the magnetosphere is no longer there to prevent the crew from possible coronal mass ejections which would probably kill the crew, but this issue must be solved one day if a Mars mission were to be even considered.

I could definitely see a JWST maintenance mission being a convenient excuse to practice further than LEO operations for crews. But of course NASA is not going to be interested in the idea if the mission fails so for now its "no chance".

18 minutes ago, vlaiv said:

Ok, I see it now.

Pink circles are due to reflections. Anti reflection coatings are usually optimized for visual part of spectrum and will now work well on say IR part of spectrum.

These are however not chromatic aberration - they are simply filter reflections (or maybe other optical element) - one that has coatings for visual part of spectrum and these reflections are in IR part.

How can you tell between the 2? Looks a lot like CA but just red instead of the usual blue. Also, if it is just reflections this would mean that some correctors might not have this issue if they are better coated with infrared in mind. I doubt the latter is true for me, since the Maxfield isn't that great of a corrector anyway.

4 minutes ago, Pitch Black Skies said:

Do you think it will make much of a difference in placing the UV/IR filter just in front of the camera sensor versus at the end of the coma corrector?

I'm thinking if the coma corrector isn't significantly bending the light, it shouldn't make a huge difference?

I suppose the camera doesn't care whether the IR is in the coma corrector or not, as long as its not getting all the way to the sensor so not important how far the filter is. Assuming no vignetting of course, but it is a 2 inch filter so not an issue.

36 minutes ago, vlaiv said:

As has been pointed out - UV/IR cut filter is needed to achieve true color image (or rather - to have a chance to achieve it).

I am planning to shoot the Coma cluster of galaxies whenever Coma Berenices rises a bit higher and was hoping i could squeeze in the extra signal from without the filter. Its not a particularly colourful target so might not be an issue. Ill test it first and see if i could get away with not using the filter as i could really use the extra QE. But if true color suffers too much, i wont risk it.

39 minutes ago, Ags said:

Light leakage in the IR spectrum can really mess colors. Here is a worst case scenario - with the IMX 462, if you do not use an IR cut filter you are really imaging in IR with a little bit of color data added. Your "blue" channel would be mostly IR signal.

If im not mistaken this particular camera has been designed around IR imaging? Mine is not nearly as efficient in near IR. Would make a superb Lunar camera though. I wonder if guiding would also be better with IR pass?

8 minutes ago, Pitch Black Skies said:

I think I'm confusing chromatic aberration with star bloating and halo's, as seen in John's image.

The pink starbloat is due to chromatic aberration, at least thats what it looks like. You can see the diffracted spider being out of focus and dark in the middle, not unlike a very out of focus shot. In that example a reducer of i believe around 0.7x is used with the Hypernewtonians and so the effect is easily noticeable. With my 0.95x? Remains to be seen (if the filter ever comes out 🙄). That particular star is also an M-type star (cold surface temperature, deep red) so it radiates strongly in infrared also, so this is probably the worst case scenario.

Sounds like a focus issue if you can see an image without the eyepoece but only the floaters in your eyes (normal btw).

Try to lift the eyepiece out of its holder and hover it outwards. Does the image get better or worse? If you do reach focus at some point you might be missing a piece somewhere. Just to make sure, but you do have the diagonal in the back of the telescope and the eyepiece in it? 

The Moon is very bright so youll be surprised how short the exposure time has to be. Set the camera to manual mode and ISO to the minimum. Try out different exposure times until you dont overexpose the bright parts of the Moon. Alternatively the "aperture priority mode" will also probably work. In that mode you choose ISO and the camera chooses the exposure time to be what it thinks is ideal. It works for the Moon a good chunk of the times.

Preferably underexpose rather than overexpose, since you cant recover detail from a fully white pixel but can stretch the darker pixels to appear brighter.

Mini PCs come and go from vendors all the time so its hard to recommend something that you buy a while from now. But the basics would be at least 8gb ram and an SSD, and running WIN10. Any CPU basically works so dont sweat it that much. The key part here is the ability to run the thing off of USB C fast charge to work with battery packs. This is not always mentioned in the sales ad so takes a bit of research.

Mine has an old i5 and 16GB of ram and it works for everything related to capture, but it probably doesnt have to be as good as mine.

1 minute ago, alacant said:

Hi

It's under Image Processing -> Colour Calibration -> Photometric colour calibration

HTH

If you dont like the color calibration result, try ticking off Auto and set the catalogue limit mag to a higher value? This way more stars will be used, assuming suitable stars are found in the image. I try to look at my image and see at which magnitude (referring to stellarium) the stars are still well resolved and not that noisy and choose that. Usually with mine i end up using down to mag 16 or fainter. Sometimes there is a difference, sometimes not, but worth a shot.

16 minutes ago, powerlord said:

Very nice. What's this photo database in siril u mention? Sounds interesting.

I would assume this refers to the Photometric color calibration tool in Siril. The actual photometric data comes from either NOMAD or APASS surveys i think.

Absolutely yes, in fact autoguiding is more common than not autoguiding. Not guiding will limit your usable exposure time to quite short ones, which will depend on how good your particular unit of EQ3 is but generally probably best to avoid exposures over 30s if you want to have most of the frames be usable. Since you are already gearing towards having proper PC control of the whole rig, you have done most of the job already.

The only things you do need to buy are a guide cam, guide scope and some cable to connect the mount to the PC. And get used to some software of course, but its not super difficult.

This is probably the most common camera for guiding: https://www.firstlightoptics.com/zwo-cameras/zwo-asi-120mm-mini-usb-20-mono-camera.html . I have one and honestly there isn't much to say. It does its job just fine.

For the guide scope you have lots to choose from and its up to you how much you want to spend on it. Spending extra is mostly a convenience thing, not something that gets you better performance (for the most part). A generic 50mm finderscope converted to a guidescope with an adapter will do the job just fine. I personally found the finderscope style rotating lens cell focuser annoying to use so i bought an actual guide scope, but this is not something that has to be done. 50mm finders are cheap and i would assume you can find a used one for sale every now and then.

For the cable, it depends. I think the newest model of EQ3 PRO might have a USB port on the handcontroller and/or main control box, but im not sure. My EQM35 has one and the mounts are quite similar in design. If thats the case, any USB2 printer style cable will bridge the PC to the mount just fine. Plugging the USB cable to the hand controller will let you use both the handcontroller and your PC to control the mount. This could be beneficial, but if youre going to only use a PC to control, then not that big of a bonus.

The other solution is to get a USB to serial cable that plugs in to the hand controller port of the control box, note that this means you cannot use the hand controller anymore at the same time. https://www.firstlightoptics.com/sky-watcher-mount-accessories/lynx-astro-ftdi-eqdir-usb-adapter-for-sky-watcher-eq5-pro-heq5-syntrek-pro-az-eq5-gt-az-eq6-gt-and-eq8-mounts.html

The second suggestion is probably the more common one, and many people find the USB to serial cable to be more reliable than the on-mount USB, but personally i prefer the first choice.

Remember that even if the spacecraft itself works perfectly, the launch vehicle can still malfunction. There is no such thing as a perfectly reliable rocket so it could turn into a 10 billion dollar fireworks show.

There could be frost developing on surfaces other than the objective lens, even inside the tube if you have moisture in there for some reason. I find a thin layer of frost develops quickly and is difficult to see by eye but the camera will pick this up as a dimming/bloating effect.

How do you handle the gear after shooting? Do you open all the caps for several hours to let moisture out before putting the gear back to storage? If you dont, you could have moisture lingering inside the tube which sets as frost to a corrector/filter/inside of the lens or whatever and wkuld be difficult to spot with the objective lens being dry to the outside.

Looks like there might be a clear night in the next few days so i could test the effects of filter and no filter at F4.2 just for curiosity's sake, IF i were able to free the filter from its prison.

I have it sitting in one of these: https://www.teleskop-express.de/shop/product_info.php/info/p10857_TS-Optics-M48-Filter-Holder-for-mounted-2--Filters---Length-15-mm.html

Dont really know why i got one to be honest, i could have just screwed the filter to the coma corrector to begin with. I thought this looks sturdier than filter drawers so probably better and since i didn't plan on changing it or ever using other filters i didn't think more of it. But now the filter prison works against me pretty bad. There is nothing to grip in the inner holder ring so i really cant come up with a solution to non destructively take it out. Perhaps i could drill 2 holes to the inner ring and fit a tool of some kind in them to get a better grip, but i would risk destroying the filter in the process. Well, ill throw it in the freezer once more. Maybe it changes its mind and wants to unstuck itself.

The 150PDS on an EQ5 PRO would probably do most of the things you want, but be 200 pounds over budget. I dont know what i would choose were i in your shoes, since i understand the appeal of doing a bit of everything. But try not to undermount whatever scope you get, it will be frustrating to use and you might end up hating it.

I also would mention what @Cosmic Geoff wrote about the setup time. My 200mm newtonian and full astrophotography setup takes somewhere around 30-60 minutes to setup to a point where imaging starts after placing the tripod on the ground. Could be as long as 2 hours if the scope has to cool down first.

I would build a desktop PC for processing and get a cheap and small scopeside minipc for capture.

Chances are the combination would still be better value for money than a laptop. I wouldnt want to use a laptop in the field or for processing, so this is a no brainer for me. If you dont want to tinker with tech and must get a prebuilt, the value gap is probably smaller, but processing will always be better done on a desktop PC due to thermal limitations in even high end laptops throttling power a lot.

Cant help with the switch problems, but thought id say that without regulation of some sort you will probably run into power problems faster than you would imagine. Just an unregulated "dumb" battery might read 12.75V now, but will drop below 12V really quickly once you start to draw power from it. Its entirely possible that your mount starts having problems slewing in under an hour. Especially true if its cold outside, you can get under 12V from a battery that still has most of its charge left and there is really nothing you can do about it other than have some sort of voltage regulation going on.

38 minutes ago, vlaiv said:

I've written so many times about this subject that it sort of feels like repeating myself

Every time you do, someone learns valuable info that seems to be difficult to come by. 

Perhaps there should be a BIN sticky thread somewhere? Pixels get smaller and smaller so binning is just a necessity for most folks. OSC is also alive and well and like you said, not the same as mono.

@vlaiv has tried to explain it to me several times and in various threads, but im not sure i "get it" yet fully. From what i understood on the matter OSC binning is not the same as mono bining and the data has to be treated accordingly. ASTAP has a binning option that can be used after capture and works for my OSC data, but i wont be claiming i understand why.

Another option is splitting the calibrated subs to their individual channels instead of debayering with interpolation, which results in 1 R, 2 G and 1 B subs that are in their actual resolution of capture which is pixelsize x2 since only every 4th pixel contributes. Then stack them as mono subs and process accordingly. I tried this as a proof of concept but since i am shooting hundreds of subs per target i am really not (yet) willing to do this. Maybe once i get a new mount and can take longer subs. 

@iantaylor2uk I thought pure mirror systems fold light of all wavelengths pretty much the same. Not exactly the same, some reflection graphs i have seen have a drop in ultraviolet and infrared, but that shouldn't effect the focal point. So the chromatic aberration in the other example is from the coma corrector lenses, both from the fast focal ratio lightcone entering at an angle and from the lenses being curved themselves.

I cant really shoot without a coma corrector with the F4.5 primary, its just too messy already quite close to the center. But just out of curiosity i might try without the filter to compare results.

The Maxfield 0.95x corrector isn't all that picky about the distance it seems, i broke one adapter and had to swap it for a few others i had lying around and i ended up being 1mm short. Couldn't spot the difference, so the filter thickness is probably also not that important to take into account. Also, its difficult to tell how much spacers are needed when the corrector doesn't correct all the way to the edges. Spot sizes in APS-C size fields are noticeably elongated with mine.

You may find that the EQM-35 does not perform all that well, at least probably not completely trouble free. If you plan on shooting unguided with it you should definitely "train" the periodic error correction in the mount. My mount came with a not very helpful PE curve out of the factory that didn't seem to do anything to the periodic error. Training it can improve things quite a lot, and for your 6 arcsec/pixel resolution should work well.

Read through the manual, there is a section on the periodic error in there. Basically you should point the mount somewhere south to as close to DEC 0 as possible, but still high in the sky, so depending on your latitude and location might not be all that close to DEC 0. Center on a star bright enough to be visible in live view, zoom in on the star as far as you can and then manually guide the star for about 8 minutes if i remember correctly? The better you do this the better your results will be in the end. If you dont do this, you shouldn't expect exposures longer than a minute to always have round stars as the periodic error can be quite aggressive on the mount.

Picture looks pretty good for what it is, an untracked short exposuretime from light pollution 👍. Although your list does not mention flat frames, which would be the most important of the calibration frames so definitely look into that.

33 minutes ago, CCD-Freak said:

You can put it on the front of the coma corrector and it might be the best place for it so that the UV and IR do not enter the optics of the coma corrector.   I often put it on the nose piece of my field falttener when I am using refractors.

 

 

This would be the plan, if i can take the filter out of its holder. Thoroughly stuck this one, in the freezer it goes for a heat treatment 👍.

So the filter stays, one way or another.

Any opinions on the filter placement then? Does it matter whether its between the coma corrector and camera or before the coma corrector. My corrector has 2 inch filter threads on the bottom where i could also mount the filter to free up some space in the already narrow 55mm backfocus between the corrector and camera. My gut says it doesn't matter, or why would the thread be there in the first place, but i could be wrong.