Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

MercianDabbler

Members
  • Content Count

    20
  • Joined

  • Last visited

Community Reputation

4 Neutral

About MercianDabbler

  • Rank
    Nebula

Profile Information

  • Location
    Mercia
  1. Thanks Tony. I was judging by the preview on the camera screen plus the histogram rather than the raw image. I'm used to raw images looking pretty dull. Looking at the histogram on its own it doesn't look too bad, the 'hill' being to the right of centre with no obvious sign of clipping. Maybe the longer exposure would have been better but having the whole frame in the preview looking so bright looked like the wrong answer to me. When I've been out under darker skies the preview looks much more like the finished photo but I'm not really sure what is normal for doing lots of frames under LP.
  2. Thanks Tony. That certainly looks better than my efforts. Any chance of knowing what steps you used?
  3. Thanks Micheal. I'd be interested to know whether folks think the gradient is purely from light pollution or if something else is going on. I've attached my first and last flat, again shrunk to quarter size. Looking again, I'm not sure there was too much amiss with the earlier flats. I guess it could be the floodlight - it wasn't lighting up the scope but it was lighting up everything from perhaps 10ft above ground level so I suspect there was some back scatter. I shall definitely try again with more exposures and without any sensor shaking in between lgts and flats. TBH I thought that 30 frames was a lot. I was quite pleased just to find some evidence of M33 in the shot since I did not see it visually at any point in the process. I might attach the camera to the SP102 next time. Now I at least have a photo of the star field so I should have a better clue how to find it even if I can't see it.
  4. I'm trying to do a bit better at AP and image processing. These are not my first attempts but previous images have used either just a single frame with a high ISO or stacking a very small number of frames and nothing more sophisticated than Picasa for image processing. The frames were taken on 18th Nov in my garden. Clear Outside says I have Bortle 6 sky but I'm wondering if it is even that good. M33 was pretty high compared to the other things I attempted on the same night. The photos were taken with an unmodded Canon EOS 70D through my ST80 piggybacked on my Vixen SP102 using the Super Polaris setting circles to find M33 and its RA drive for tracking. I could not see M33 visually through the SP102 (or my 10x 50s)... so I used the ST80 for the photos to give me a better chance of finding the target. Reading up on ISO levels turned up a recommendation to use ISO 1600 with the 70D. I went up one 'stop' to 3200 because it was pretty gusty that evening. 31 light frames of 10s at ISO 3200 (more exposure was producing a very foggy looking frame which I thought did not bode well for pulling any detail out. Maybe that was an incorrect call but I needed to pick a setting and get on with it) 13 darks, 15 bias. The darks were done in between the lights because a neighbour's floodlight kept coming on so when the light was on I put the cover over the scope and took darks. It's likely that some of the lights were affected when the light came on in mid exposure. The camera was left attached to the ST80 and the focus left alone when I took everything indoors. Originally 20 flats done with the T shirt method the following morning but cut down to 2 because I suspect most of my flats had a gradient in them perhaps from being aimed at the sky too close to the house. The last few had a different aim but then it started raining causing me to duck inside for cover. I did note the camera doing it's sensor cleaning routine when packing up in the evening... I wonder if this negates the dust fixing potential of taking flats the next day? Dark flats... None. I've read about those but don't really understand the value of them. Anyway, some pics. I'm not looking for others to do my processing for me thanks, just to get some pointers. Stacking was done with the latest version of Deep Sky Stacker. I didn't mess with the settings. The first attempt was done before I'd looked at any post procesing tutorials and with my pre-existing version of GIMP (2.8 IIRC) which will only deal with 16 bit TIFFs. The uncropped result after adjusting levels is below. The histogram looked very quantised so clearly 16 bit is not ideal. I had to reduce this image to 1/4 size before posting because the full size JPEG export wound up at 27Mb. The most obvious issue with this is the amount of fogging in the lower right half of the frame, the peculiar colour cast of the whole scene plus the amount of coloured speckly noise in the background. Then I installed GIMP 2.10 and worked with a 32 bit TIFF after reading some tutorials (mostly not about GIMP but a recent M31/M33 thread on here including GIMP and ImageJ). My steps were as follows... crop away the edges where the stack is not fully overlapped colour balance - use the levels tool and fiddle with mid point triangle. Initially tried to fully overlap the RGB histogram 'humps' but this was too much so then I did it less aggressively and eyeballed the resulting image. cloned the layer to start working on removing the skyglow despeckle at 15 radius use the heal tool to clone over the bright area left by the galaxy, cloning at right angles to the gradient Despeckle had left a lot of strange looking banding artefacts so I used gaussian blur with radius 60 to smooth these out use levels to temporarily pump up contrast to check the skyglow layer put skyglow layer above main image and set mode to difference, set opacity to 99% because it looked a bit too severe. I also tried subract mode but that looked more strange. merge skyglow and image layers lasso galaxy etc and apply unsharp mask, radius 1 final crop export to JPEG at 98% quality The background is a better colour so my first try at deleting the LP fog seems to have worked but I can't say that I'm hugely excited by the final result. Any attempt to tweak it further with curves brings out some odd looking noise in the background. It also seems to have lost some of the outer parts of the galaxy that were visible in my much cruder first effort. I did not use ImageJ. I read the other thread and it seemed to be used there (mostly??) for producing an artificial dark... but I had darks. Did it do something else that I ought to be doing? Any pointers gratefully received!
  5. I don't think anybody said M57 yet, so... M57 Lyra is often pretty high from our neck of the woods and M57 is a lot less of a fuzzy thing than many other objects. I'd suggest getting a bit more involved in planning your own target list, for example look at the Messier list on Wikipedia and sort the table by constellation. Figure out which constellations are favourable and pick some easier Messier objects to start with. The Messier Marathon Planner http://calgary.rasc.ca/darksky/messierplanner.htm is handy because it tells you which ones are easy to spot and which are difficult. You don't need to do a marathon to get some good info from this site. For me, star hopping to a target is part of the fun (assuming a successful outcome anyway), albeit now using Stellarium on a tablet rather than a paper sky atlas. Stick with it
  6. After much more reading, agonizing, indecision and changes of mind I have just pushed the button on a 15mm Vixen SLV. After initially thinking that I would keep the Skywatcher EPs out of the calculation I decided that that the SWs are probably not the worst ever bundled EPs and an EP at a given focal length is better than no EP. This way I will have four EPs (of varying quality) with reasonably well spaced focal lengths. I was really torn over whether to go for a Hyperion and it was a close run thing but I think their size and weight counted against them with me... plus the 17mm Hyperion seemed to be overlapping very much in terms of TFOV with the 26mm Meade which is my best EP at the moment so I don't want a new EP that is going to persuade me to use my favourite one less often. Convoluted logic and probably the wrong answer but we shall see how things go when I have some suitable weather after Xmas. Naturally this exercise has given me quite a wish list of further upgrade options... but that's for another day. Thank you again to everyone who offered advice.
  7. Yes that is an extreme (but still useful) example... thanks. I'm familiar with the wallet emptying potential of my hobbies ( I have others ) so I shall try to keep myself under control. My local light pollution also acts as a natural brake on my desire to sink a lot of time and money into astronomy but at the moment I'm feeling that I've blown the dust off the scope this Autumn and refreshed my knowledge of how to use it so some further investment would be a good thing. To come back to one of my original questions, the Hyperion 24mm would give me 1.63 degrees TFOV vs 1.37 for the Meade 26mm (correct??). Somewhat counter intuitive - my simple logic had suggested that 24mm would be a small step backwards from 26mm and I should be seeking a longer focal length but it seems that my simple logic was wrong. I can't see the field stop size quoted for the zoom so I'm not sure how that option would measure up against the TFOV question at 24mm. The Hyperion with its wider field of view and slightly lower price is looking like a better option than the Vixen SLV just now but am I missing someting? - Does the SLV have selling points that the Hyperion lacks? At the moment I'm tending towards individual eyepieces rather than a zoom - my immediate plan would be to buy just one to fit in between the two Meades that I already have. Going down the zoom route with FLO immediately suggests going for their zoom + Barlow bundle... which puts the price up to 235. This price might not sit so well on the Xmas list. I get the point about the reduced need to swap things in the dark but to swap between, say 6mm and 24mm would still need the Barlow to be added or removed in the dark.
  8. Hmm... I've been reading up on apparent FoV. I now understand how it is calculated/measured and what it means... but I don't think that's really what I want to know. I have less understanding on what is good and what is not good in terms of apparent FoV. I get the feeling from the previous replies that 'more is better'... always?? My current eyepieces (or rather their current equivalents from Meade) both state 52 degrees apparent FoV. Is this good or bad? I'm somewhat puzzled by the idea that both the 6.4mm and 26mm Meades have the same apparent FoV because they are so different to look through... but me being puzzled by astro kit specs is not really news. The Baader Hyperions state 68 degrees and say this is 'regarded as ideal' (they would say that, wouldn't they?)... other (higher priced) eyepieces have more... so is more than 68 really 'not ideal'? The Vixen SLVs state 50 degrees and 45 for the shorter focal lengths, so less than the quoted numbers for my M4000s. Would I notice a difference at 50?... at 45? I hadn't looked at the Hyperions before. They do look interesting, particularly the ability to attach a camera. With my engineering head on I can't help wondering if hanging a Canon DSLR onto an eyepiece held by a single clamping screw on the focusser tube would be wise though. Am I understanding the Hyperion blurb correctly? - would I need 2 inch filters or could I use 1.25 inch filters? Sorry for the scattergun questions
  9. Thanks for your input Don. I must admit that I have not yet understood what apparent FOV is all about... and therefore (I guess) what the value proposition of wide angle eyepieces is - clearly I need to do some more reading on that point before committing to spend money. I did find a used M4000 26mm of similar vintage to mine on the net this afternoon and was a bit surprised at the price tag. Collectable eyepieces eh? - news to me! Anyway I'm not planning to sell mine on because it's still doing the job that I bought it for. Sounds like I shall steer clear of the later model M4000s. Most of the TeleVues seem to come with a fairly hefty price tag. I won't say never but I'm not convinced at the moment that I want to go there. The Vixen SLVs seem well regarded on here and their price tag is only just into three figures (GBP). Anyone care to comment whether one of those would be a good match for my scope in the middle focal length range? (probably 9, 12 or 15mm).
  10. I've been reading up on eyepieces recently and trying to work out a shopping list myself but there are so many variables that I think I'm just going around in circles. My scope is a late 1980s Vixen SP102 (1000mm F10) with a 1.25 inch eyepiece fitting. I currently have two decent eyepieces - both Meade 4000 Super Plossls - 6.4mm and 26mm. I gather that 'Meade 4000 series' covers a bunch of different generations of varying reputation. Mine are late 1980s and made in Japan. The 26mm is nice to use. The 6mm less so - not enough eye relief and tricky to get my eye lined up correctly to see through it. I also have the bundled eyepieces that came with my Skywatcher ST80 (10 and 25mm) but I'm not really counting these in the equation. I also have a 2x Barlow from the same bundle. When I've used the ST80 as a grab and go I've always used the Meade EPs on it. I look at all sorts of things but my favourites are galaxies and nebulae... but when planets are favourable then I look at those too. I'm more of a sightseer than a dedicated observer. So, what is missing? 1. Can I get a wider field than I have with the 26mm? Probably not much? I think this has a 23.9mm stop and 1.37 degrees TFOV on a 1000mm scope (and 3.42 degrees on the ST80) 2. Something in between like 10, 12 or 14mm ish. Another Meade 4000 or avoid like the plague? 3. Is there a better option for the high magnification EP that provides more eye relief? 4. Is there any point thinking about a better Barlow or better to save the money for EPs? Budget-wise I'm thinking that I don't want to shell out for top grade eyepieces for my ageing mid range scope. It's unscientific but EPs that are well into 3 figure prices feel like too much. New or used are both options. I don't think that fitting a 2 inch focusser is justified in terms of cost or effort and have no plans to change scopes. Meade 4000s seem to be very numerous on a certain auction site compared to other types. Is that because they just sold more in the first place or because owners are keen to get rid? Thanks in advance.
  11. Answering my own question I think I've mostly figured out a way to do it now... 1. Look up the RA of Polaris now 2. Look up the RA of Polaris in 1986 3. Follow the Vixen instructions but line the date up with a time on the RA dial equal to UCT less the difference between 1 and 2. The fact that I'm in the UK helps here because I really can't get my head around the longitude part and how you are supposed to dial in the time for other time zones. 5. I have set the dial on the eyepiece to 1.5 degrees West. 6. I think that should put Polaris exactly on the line. The reticle has a bit more than the manual suggests, including a graduation at 40 minutes of arc, so judging 39 minutes is pretty easy. 7. Double check that the view in the reticle roughly matches what the tablet app shows (so far it seems to work!) Does that seem right? I have some coordinates for Polaris in 1986 but I'm not sure how accurate they are. Does anyone know a good source for this info?
  12. I've been meaning to get around to figuring this out. Having re-read the manual several times I don't think I fully understood how to do it in 1988 when I bought the scope and now there is the additional complication of Polaris having moved beyond the positions shown in the manual. On the plus side I have an Android tablet and access to modern polar alignment apps but I can't say that I really understand how to use the two together. I've been struggling to ask this question in a simple way and have failed, so apologies for that. Hopefully someone will stick with me... The manual is somewhat terse in its descriptions... Whaaaat?? So line the RA hours and minutes for now (in local, DST or UTC??) up with the current day and month... I think?? Here are the dials... Skipping the straightforward stuff about levelling and uncovering the polar scope... finally the manual explains what to do with the reticle... My longitude is 1.5 degrees west. Let's say it is tonight (23 Oct 2020) at 21:00 BST. I have the option of using a tablet app. Most of these show a view that looks like the reticle, but my reticle was designed for the position of Polaris in 1986. It seems to me that this is solveable but I'm unsure which bits of the SP instructions are redundant if I use the tablet app. The tablet app on its own doesn't seem enough because I still need an accurate way to transfer the setting from the picture on the tablet to my alignment scope. One app (PolarFinder) provides a 'HA' number (I guess this is the Hour Angle for Polaris) and a 'P.Scope' number (no idea!) but the help suggests transferring the alignment by eye and does not explain what to do with these numbers. Can I rely on 'up' on the tablet being the same as 'up' in the scope? The big circle in the SP reticle is (if I understand the diagram correctly) 48 minutes of arc in radius, which isn't right for 2020. I'm guessing that the tablet app shows a circle that is correct for 2020. I think this should be 39 minutes radius given that the decl of Polaris now is +89° 20' 56.9" The change in Polaris position shown in the manual seems rather more than other sources suggest - I've read 1 minute in 5 years. Is the manual wrong? Another option (I hope!!) may be to just use the hour angle for Polaris from Stellarium but I'm unclear how to make this work using the scope dials. I'm hoping that I can figure out how to position the reticle so that Polaris should be exactly on the line towards the smaller circle but it seems to me that if I follow the instructions to the letter then that would have happened in 1986 but it won't work in 2020. Some bits of the instructions need to be ignored, but which bits? Then if I get Polaris onto the line I just need to judge where 39 minutes radius would be. Thanks in advance.
×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.