inFINNity Deck

Yes, at the upper- and lower-right I do see ampglow in my masterdarkflats: Above image is stretched and resized, the original fits is here. Recording with ZWO ASI1600MM Pro Cool @ -20°C, 67.1 seconds exposure. Nicolàs

Hi @tooth_dr, Yes and no: Yes, because they add noise (depending on the amount of darks taken), and no as they will remove amp-glow. A few years ago I did a test on the amount of darks, compared images corrected with 25 and 500 of them, to find out that 25 sufficed. The write-up of that test is on a Dutch forum, but should translate well when opened in Chrome: https://www.starry-night.nl/forums/topic/ruis-in-de-cmos-cameras-metingen-en-berekeningenn/#post-21015 Nicolàs

Hi Cyril, thanks for this interesting read! When I take flats (SW Esprit 150ED with ZWO ASI1600 Pro Cool and ZWO filters) I always do it in one sequence. To avoid too short exposures (which will cause banding due to the flickering nature of the flat panel I use), the exposure for luminance starts around 1s, as a result of which Red is taken with an exposure time of 2.5s, followed by Green (4s), Blue (11.5s), H-alpha (34s), S-ii (59s) and ending with approximately 67s for O-iii. In your article you wrote "However, a flat is an image taken in full light, at times very short generally less than 5s." Clearly this is not the case in my workflow, while you imply that masterdarkflats are useful for longer exposures. So I would like to turn the question around in the hope you can elaborate on that: Upwards from what exposure-time should we use masterdarkflats? Nicolàs PS: the reason for my workflow is that I have an observatory and thus can permit to 'fire-and-forget': when I come back after several hours all subs have been taken. Same for darks...

My C11 is a C11 EdgeHD with mirror-locks. It could be that other C11s use other threads. The only other thing I can imagine is that, because I bought my SCT second hand, that the previous owner may have changed the threads, but currently all four currently are #10 24TPI. 32TPI converts to a pitch of 0.79mm, not a standard metric thread (there are metric fine threads that have this pitch, but those I do not expect on this scope). Nicolàs

I have seen multiple Esprit 80EDs with pinched optics and the company in the link I posted earlier today has seen several as well, they even have designed a new lens-cell for SkyWatcher to mitigate the issue. An aperture mask may indeed remove certain artefacts as I described above (last Friday at 21:11). But the aperture should be extremely smooth to avoid new artefacts arising as I shown in that article. I made mine of aluminium and polished it. Nicolàs

Hi Andy, perhaps the following article is good to read: http://interferometrie.blogspot.com/2014/08/esprit-tuning-how-we-finetune-esprit80.html As can be seen there are two types of collimation screws: So the lens-cell collimation screws are the ones that hold the lens-cell and are there to be able to set the whole lens-cell perpendicular to the optical axis. The Lens-alignment collimation screws (here they are in sets of 3 as this is a triplet) are there to hold the lenses in places and to arrange their mutual alignment within the lens-cell. In neither case is it possible that those screws enter the light path. The lens-cell collimation screws are not even within the tube and are parallel to the optical axis. The lens-alignment collimation screws do move inwards, but cannot enter the light path as if that were the case, light could pass between the lens-cell and the lens (or the lens is missing). What some manufacturers do, is using small spacers between the lenses (taken from https://www.cloudynights.com/topic/647909-refractor-doublet-lens-spacer-material/): These are able to protrude within the light path if not well cut and/or placed. They can also explain why the dark spikes are only 2 obvious ones and that they are not separated by 120 degrees. Nicolàs

Just for the record and to avoid confusion: this is indeed what I meant with pinched optics. So the lenses get pinched between the screws. Loosening the screws should be done with utmost care to avoid that the individual lenses lose their mutual positions. You also want to avoid that they get too loose. Nicolàs

When seriously dirty I clean my ZWO cameras (ASI1600MM, ASI174MM, ASI 290MC) using Baader fluid and that works like a charm, no harm done. Spray it on a micro-fiber cloth and use that to wipe the chip. But I only do it when really dirty (over time they tend to get deposits of the grease that is used to seal the cameras). For normal cleaning I recommend one of those power blowers as John suggested. Nicolàs

That is just to avoid that we get bored too soon... 😉 Nicolàs

BSW and UNC are more or less interchangeable, but not exactly (different rounding of the threads and minute difference in diameter). Being made of aluminium it is no problem inserting the wrong type in the holes. I noticed that on my C11 a variety of threads was used: UNC, BSW and metric, but I cannot say for sure which ones were original. As BSW are very hard to get at these sizes here in the Netherlands I decided to order UNC for all non-metric screws. Nicolàs

Hi Ossi, officially these screws are 10-24 (3/16), so number 10, 24TPI, 3/16" diameter. I uses them for all four holes if I remember well. The length depends on whether you use the original orange dovetall or an ADM one. Nicolàs

Hi Oymd, I have listed them here: https://www.cloudynights.com/topic/666441-celestron-c11-edge-hd-bolts/?fromsearch=1 Nicolàs

Hi Philip, that Sadr-region image looks much better indeed, I cannot find those same dark beams in it. A dew-heater could possibly help when wrapped directly around the lens-cell. Instead we commonly use them wrapped around the dew-cap, just to warm the air directly in front of the objective lens, reducing the chance that the dew-heater has a significance effect on the cell. With one of the ED80s I tested I first cooled it to around 4°C by having it in the fridge for a whole night. Then next morning I let it warm-up to room temperature in front of a collimator with the following result: The left image shows three dark spikes at about 4, 8 and 11 o'clock. In the right image they are absent. This is of course the difference of 16°C, a dew-heater is unlikely to produce such a difference. The method, however allows us to test. So what you could try is to have the scope indoors fully prepared to image, then (once at room temperature) take it outside and immediately start taking images and continue to do so until the scope is fully cooled-down (that ED80 I tested took just over two hours to reach equilibrium). Nicolàs

Hi Malcolm, there could be another culprit involved: an OAG. If you use one and it is too far inserted, it may cause these kind of diffraction patterns. But as you also made a test with a 200mm lens, I guess you were not using an OAG... Nicolàs

The best test for proving it is camera-filter reflection is changing the distance between them and see if they grow or shrink accordingly. I had a 10mm spacer between the flattener and the filter-wheel, which I could move to sit between the filter-wheel and the camera. I did it that way as not to mess up the proper camera-flattener distance, but for a test that is not of great importance, adding a spacer will affect star quality, but immediately show (or not) the effect on the halos. Good luck and please let us know what you find! Nicolàs

These are filter masks to avoid light leakage around the edge of unmounted ZWO filters. I explain that in an article on a Dutch forum (opening in Chrome should translate properly): https://www.starry-night.nl/forums/topic/maskers-voor-zwo-efw/ As can be seen they do make a huge difference in flats quality. Nicolàs

Hi Tom and Philip, I disagree that this is normal with Takahashis. Yes, the FSQ85 shows similar patterns, but those are caused by internal reflections between lens surfaces, are always in straight lined pairs and rotate around the centre with the pair being perpendicular to the line between the star and the centre of the image: https://www.astrobin.com/full/pmh3a6/0/ What we see here in Philip's image can have two causes: pinched optics or uneven/non-smooth aperture. I have seen the latter in three Esprit ED80s I examined and described it in an article on a Dutch forum. Opening the article in Chrome should properly translate it: https://www.starry-night.nl/het-verwijderen-van-artefacten-bij-een-refractor-met-een-brilletje/ As I describe, the uneven halo can be corrected by stopping down the aperture by 1 or 2 millimetres with a bespoke made field-stop. Pinched optics can be checked by using the scope at a higher temperature, if the dark lines become weaker it indeed is a matter of pinched optics. Nicolàs

I agree with Mark that it most likely is reflection between the camera and filter. Increasing the distance between them will make the halos larger and weaker, so perhaps that is a solution. Also the ZWO filters have a front and rear side, as indicated by ZWO, and it is useful to test which side works best (I found it quite difficult to test it otherwise). I have done those test with the old style (pre June 2018) filters and turning them around made a difference (for the test I simply turned around the whole filter-wheel). The old style filters also showed multiple concentric halos in H-alpha and S-ii, which are absent in the new style ones. Details of my test are on this Dutch forum but translate quite well when opened in Chrome: https://www.starry-night.nl/forums/topic/halos-en-zwo-filters/ Nicolàs

Please keep us posted on the results, I am always intrigued by these matters, so would like to learn about this one. Nicolàs

Hi Malcolm, I combined the images and mirrored the one taken with the 200mm lens: Clearly the bright spike is not a mirrored version.... very strange... Nicolàs

Hi Malcolm, at least that shows that the bright spikes are not caused by the scope. Could you produce another image with the scope, but with the camera at a different orientation (or even several images with various orientations)? If the dark spikes still are perpendicular to the bright ones, then we know for sure that all artefacts are caused by the camera. I have no experience with DSLRs in astro-imaging, so the next could be totally wrong/rubbish: I presume the camera has a flip-mirror? Could it be that it does not fully fold away and that we see reflection of it? How come the orientation of the bright spikes when used with the 200mm lens is mirrored to those when using a scope? Nicolàs

That is indeed the case. I have been considering buying a FSQ85, but found that quite a few images on Astrobin taken with that scope suffer from those dark lines. Those dark lines, however, rotate around the centre of the image, see this one for example: https://www.astrobin.com/full/pmh3a6/0/ In contrast the dark lines shown in Malcolm's image seem to have a perpendicular orientation to the spikes and thus a fixed orientation (provided that this is true all over the image, which is hard to assess) and thus have another cause. Nicolàs PS: I ended up buying a SW Esprit ED80

Did you check the scope from the front to see if there is anything protruding into the scope? The type of spike indicates that there is a single foreign object in the light path. This could be a screw that is too long. This type of spike will also occur when imaging along an edge like the slit of a dome. Nicolàs

Oh, and this is the raw stack from AS: So still blueish. Nicolàs

Hi Maideneer, yes, thanks to a gain at 435 I could get the exposure as low as 35ms (remember I used an 11" scope). And, yes, I did use an ADC. If I remember well I 'trained' myself using Mars, so a nice bright object, by adjusting the ADC and re-centring Mars using live view. For centring Mars I can use the original 9x50 Celestron guidescope. Then I examined how much my mount veered off when giving a slew-command to that object. The difference in RA/DEC I then used to get Uranus in my field of view. I then recorded 5771 frames of which I stacked 200 in AutoStakkert!3 using 1.5x drizzle. The outcome was poor, but the colour was definitely there. I did quite some processing to make it look like a planet, but definitely over-processed it to make it look a bit presentable... This is what the best frame looks like in AS3 (view @ 200%): So definitely colour in there, but not much of a planet yet. If I export that frame it is B&W (@100%): Nicolàs PS: here is Mars of that evening: http://www.dehilster.info/astronomy/mars.php#1836