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I've looked into this a lot, especially once I got a 294mc camera which is notorious for calibrating (it's in fact nothing to do with flats but the construction of the sensor glass). What I did was use around four sheets of perspex going from opal down to an almost black. Even on the dimmest setting if I'm using a UV/IR or lum filter the exposure ends up being around 1-2s which I'd still consider fast. Using a computer controller helps as they usually have an auto exposure mode that works it out automatically when it takes test exposures prior to the run. If I'm doing it manually I try to make sure the histogram peak is around a third across from the left, but this largely depends on the F ratio you're imaging at, at F2 you'll find the centre of the flat looks like it over saturates very quickly so you have to adjust accordingly. Your camera settings should be the same as the lights (gain, temperature etc) the only thing you adjust is the exposure time to get the histogram as you want it. If it's too bright very quickly you need to diffuse the light even more.

https://www.ebay.co.uk/itm/155285721776?var=455483654241 looks handy

I always wondered how large this effect is - particularly on galactic scales. For example - when computing Hubble's law - do we have to take into account relative difference between galaxy masses? Origin galaxy and MW? When light leaves origin galaxy it will be red shifted, but then when it "falls into" MW it will be blue shifted - difference between those two will be some percent of total red shift - but how large is the effect?

Are they moving or is the space expanding in which they are, its a bot of both IIRC the greater the distance the more the spacial effect.

If orbiting a black hole - one week they could be coming towards us, the next moving away Jim

I'm not so sure that matters though. The measurement of red shift is a relative velocity measurement - it already ecompases the relative information by default. If the light is redshift then we know the object is moving away from us. If you want a direction (polar, cartesian or otherwise) then you would need to specify a reference axis. You would also need to determine proper motion of the star as well. Jim

It's possible to do planetary with a DSLR but you are usually hindered by some factors: 1. The dslr sensor is quite large, so planets will appear tiny, it's one of the reasons to use a Barlow and to increase the f ratio. 2. Image capture can be slow, for planetary you need fast frame rate due to fighting the atmospheric seeing and DSLRs even at constant image capture usually cannot capture fast enough due to large file sizes and buffers which fill up very quickly. A workaround is to use video capture as you're typically "imaging" at 25fps or faster if you have adjustable shutter speed during video capture, this can also be an issue as most cameras capture video in compressed format, using a computer controller you can possibly bypass this and capture raw video. 3. Due to 1+2 focusing can be an issue. The connection you'd use is the usual 1.25 inch visual back of scope > barlow > t nose piece > t ring > camera. Some eyepieces have male m42 threads under the rubber eyecup which you can screw the t ring directly onto but they are few rather than the rule. With planetary cameras you can decrease the FOV of the cameras resolution (also called ROI or region of interest), this serves two purposes, keeping files sizes per image smaller and increasing the FPS of the camera capture rate if the camera is capable of it (I've done over 100FPS at times with a camera that can theoretically do 150, you then get into storage bandwidth issues (memory not being fast enough to keep sustained write speeds) and your storage space filling up incredibly quickly, a typical session I capture 20-30Gb of image files in around 30 mins of being outside on one planet).

If one star is a white dwarf, it could be moving towards, away from, or be stationary relative to the Earth. A strong gravitational field also creates a red shift which may be larger than the Doppler-induced one.

Yes I think you are right it's the ITF filter

wow

Curious. I very rarely find that an exposure of less than several seconds is usable with a light panel. The time required depends on the filter used, of course. Perhaps your panel is intrinsically brighter than mine. FWIW, I would suggest you continue with your current practice. Do you have any evidence that the flats you take are unsatisfactory? That is, do you see any residual gradients, vignetting, etc after applying your flats to your lights? If not, leave well alone - i.e. if it aint broke, don't fix it.

M106 taken using my Celestron C8 with Meade 0.63 reducer and a Zwo ASI 294 MC pro camera. Capture software was NINA with PHD2 for guiding (separate guide scope currently being used). A total of 239 90 second subs taken at bin 2. The subs along with flats, darks and dark flats were stacked with Pixinsight using weighted batch pre processing. All subsequent steps were performed using Pixinsight to get the final image. I am still not sure I have the C8 optimsed properly with the back focus from the Meade reducer. Additionally I have convinced myself that my flats are not right as there was a lot of vignetting and. some rather odd halos concentric to the galaxy. The capture was probably not helped by a rather prominent moon, but if I waited for clear skies and no moon I wouldn’t capture anything! Thanks for looking Ian

Just watching Cuiv's latest video from two hours ago. Not only is graxpert free but it now has a noise exterminator feature. Gonna give it a go

I have been using flats for several years but recently was wondering if maybe the flats I was taking might not be as good as they possibly could. My current method is to use a light panel with several sheets of white A4 on top to dim the light source. I then adjust both the gain and the exposure time so that I can achieve an exposure time in the region of 1.5 seconds and the histogram at or around 50%. In order to see if I was doing anything wrong or if my results could be improved I had a look around the web and seemed to find some conflicting information. Some sites state that the camera gain should be the same as used to capture lights. The problem I have with this is that if I keep the gain the same I end up with very short exposure times if I am to keep the histogram at or around 50%. This then conflicts with other online advice that states that flats exposure time should be somewhere in the range of 1-3 seconds. Given I have spent hours optimising and capturing data I don’t want potentially reduce the quality of my processed image through poor calibration. Therefore What do people consider to be the best way to capture flats? Thanks, Ian

The ADC is recommended to be the last piece of equipment before the camera or eyepiece. I've never tried it in any other arrangement though to compare.

I'm not sure Andy - statistics don't lie! And what was it that good old Patrick used to say - "Every nut thinks Every other nut's a nut'! That's quoted from the book Bureaucrats and How to Annoy Them, by R. T. Fishal. (Patrick Moore). Which incidentally I've loaned to some lower than life individual who I've just remembered hasn't returned it. If only I could remember which lower than life individual I loaned it to??😕

You don't need a flattener for planetary imaging as you are capturing on axis images. You would fit the barlow into the focuser and then the camera. What is the pixel size of your DSLR to determine what strength of barlow would be best? The resolution of the planet won't be great though due to the small aperture of 72mm.

Just about managed to get round the issues of flats not working - something must have rotated. 27 x 300 sec Triband RGB wih ZWO 2600 & WO 132

I'm expecting them to be tiny but was reading a post on here from someone with same scope and the results looked good to me. Was just thinking on a 50% cloudy evening but I can see Jupiter or Saturn it'd be pretty cool Just have no idea size/type/fixing of the Barlow needed. There's a lot on eBay not read all the link but first image would be pretty incredible to get. Similar camera as me, likely bigger telescope Ty for this

Thankfully, the car owner's insurance covered a builder to do the wall, saving me a lot of effort.

Looks like a lot of hard work has gone on since the initial build, looking rather smart and very Garden Makeover too. Sorry about your BMW wall interaction, cars hitting your property is never much fun. But your rebuild looks up to your usual high standard 👍

planets are tiny you may not need a flattener if you were using a tmount with a tring to your dslr then you could insert the tmount into a barlow or screw it to a shorty barlow then put dslr with barlow into focuser on telescope i think could look at this https://www.astropix.com/html/equipment/canon_one_to_one_pixel_resolution.html

Been reading some interesting posts on here about using a Barlow on my 72ed with a dslr to image planets. I assumed a Barlow lens was very similar to a Tele converter/whatever canons stupid name is, and so 'bad' for astrophotography. Seems this is not the case? How would I include a Barlow in my image train to try this? Would I need a specific size/thread/adapter? If it went between focus tube and flattener my back focus would stay same? Also if it's possible, please point out any incredibly obvious potential issues I will be completely ignorant of. I'm struggling to Google Barlow dslr planets and get anything that shows how to connect it.

April 20th & 21st The clear Friday night developed into a clear, calm and dry weekend, so it was time to get back to the wall. I've built walls before at the Washington house. Made from modern metric bricks, they turned out so neat, that some people thought the pictures were CGI of what I planned to build. This wall isn't like that at all. The bricks are Victorian, dating from around 1860, appear hand made. Some are huge, around four and a half to five inches wide in places and none are exactly the same size, nor have flat faces. Some are bulged, some are con-caved, the ends aren't necessarily square and the proportions aren't right for the length of one brick, to work with the width of two bricks for the pillar. All of this is made laying them a real challenge. Straight and level needs to be an average, as a small level won't sit flat on any of the bricks! Several bricks broke or crumbled during dismantling of the wall, so multiple half bricks were used on the far side, below ground level. They are all being reused from the original wall, so all are stained from age or lime mortar. I may try cleaning them once the wall is finished. By the end of Saturday, I had four courses added on the front and two on the back. My back really didn't want me to go back out on Sunday, but I couldn't waste another good weather day. Another two courses were added to the front, with four at the back, though every fourth layer has the bricks laid across the wall, to tie the two sides together. It was all covered in plastic by the end of the day, as the rain came back that evening and has continued on and off to today. Lynne also gave the lawn its first cut of the year. It was still a bit wet, but had got so long, it took her two hours. I'm hoping a rotary wire brush or grinder can clean off the bricks a bit. A quick test seemed to suggest that would work, but they've got 150 years of weathering to catch up on to match the rest of the wall - which also needs pointing. Yet another job! It was nice to get back out in both the garden and observatory.

For me it's down to the details of how exactly it operates. Impossible to tell at this stage. Definitely watching it!