Seen some lovely Trifid neb pics lately so decided to post my widefield of M8 and M20 taken with my Genesis 100mm f5 scope last month. Stack of 7 frames at 4min each with my canon 300d. Was pleased on how well it came out, the full size pic is real sharp, closeup of Trifid from original, one of my better shots and my eq5 worked well after I gave it a talking too!!!... I think I have the color balance fairly good with this one too..?
I just dont understand why their is blue fringing around the stars...I am seeing this a lot on some top end refractors and dont know why when we dont see it on cheap Orion ED refractors 1/10 of the price...the Genisis is a true Apo isn't it....I could be wrong.
Besides the fringing their terrific shots Gary..well done.
lovely shots but I think Tony has a point again! The fringing detracts from the images a little, but they are reaaly nice too. The colour is an issue as I have no real idea what the actual colour is supposed to be, but then does it really matter that much?
Maybe the fact it is a f5 scope has something to do with the fringing Tony, a baader fringe killer or WO vm1 may be the answer!
Really nice shots. Without the benefit of a high resolution image my guess it's actually the blue colour of the brighter stars bleeding at their edges.. If you look at the brighter 'red' stars they have a red halo. If bet if you turn the brightness down in PS the centers would turn blue.
There are two stars about the same brightness to the right and below center obove one another and close., one has a red halo the other a blue.
Thanks everyone for the comments,
My scope would be around 15 years old so maybe thats the reason? It has always had the blue fringes even with film and the red bleedout might be to do with the IR/UV filter being removed and the edge of infared spectrum not being in focus?.. I have always wondered if a fringe killer filter would help?
I always think the stars are always a little bloated as well.
Anyone else have a Genesis with similar results?
The new ED`s and APO`s would be much better optically I say but just ordered a GM-8 mount. A better refractor is a little way off!! unless Synta comes out with a ED 120mm f7 ,(come on Synta!!) I would buy one..
Ok I was totally wrong. I did not realize that an APO was not an APO.
We are indeed fortunate that now we have so many APO's so much better than fifteen years ago. I remember when the Genesis came out! How far we have come. Being tetchy about a bit of colour is not in anybodies interests.
I still think the colours were great in these images. I happen to use the best APO ever built and lent Scott the second best (just).
The other guys have pretty much covered it. ie Great shots, pity about the blue fringes.
There are some software solutions to this problem as well.
ImagesPlus has a star size and halo reduction routine that helps. It is not perfect, but it "takes the edge off" so to speak.
Even in Photoshop CS you can use the Select --> Colour Range to select the offending blue and then use an adjustment layer to soften it a little.
These techniques, although not a cure, will improve the look of your images (IMHO)
Your right on both there Gbeal, didn`t think skywatcher had one but they do now!! but have to save quiet a few pennies for it..had a look with Houghy`s link...thanks Houghy.
I got the Genesis secondhand about 18months back as that was all I could afford and the only other choice as for new would have been the ed 80s.
Might give Itchies idea ago and play with photoshop and see if I can improve the halos a bit..
Thanks everyone for all your help and comments..
Clear Skies ..Gary
The 4" f5 Genesis SDF is not an APO; it's better!!
The SDF stands for Special Dispersion Fluorite. The Objective is a two element lens with Fluorite elements and further back in the tube there is a special two element Nagler "corrector" which give it a tremendous colour corrected flat field. So it is a four element system.
Re the blue halos etc I've never had this on any photos I've taken with the Genesis and if you check out the web you'll find many conventional film and digital astro images from the Genesis which are 100%
I can only assume an artifact of the processing of the image???
The halos are in the raw shoots straight of the camera, maybe not as bright but very noticable. Any ideas to why?, would it need a good collimation? Theres some dust in there and the lenses are in good nick...maybe I have a lemon...Gary
Don't know what the problem is but it's not collimation. The star images look pretty regular and tight. I'm wondering if it something to do with the camera filters?? Let me think about it.
Normally there's not much can go wrong with the Genesis. What's the serial # for the instrument, I'd be interested to know.
Is the 300D modded and if it is, has it a UV/IR filter? If it is modded and no UV/IR filter all is explained and it is not the Genesis. Sometimes if focus is a bit off this can happen but not at the red and blue simultaneously.
The only other explanation is major saturation of the camera sensor and this accentuates any minor secondary aberrations.
Thanks everyone for the advice, I know it is not the dew as that night there was very low humidity and took another 12 shots at M16 before dew showed at all. Merlin, the serial number is 1255 on the genesis...sounds like one of the first batch!!!
Bert, I have a baader uv/ir filter in the camera, I had a look at the graphs for the original canon and the baader filter and the uv cutoff seems very much the same except there is a small peak in the uv at about 320-350nm range.. Also the baader filter has a slightly higher transmission rate the that end.. At the red end I can understand some red abberrations as the baader gets down much more than the canon off cause so we get the hydrogen emmisions and more..and I guess most lenses are not well corrected into IR. I might give a uv block filter a go like suggested by you Merlin and fringe remover by Houghy and see how it goes..
I have put up a pic of 2 shots of stars near m42 (excuse the poor quality of the shots as that was all I could find) left is after modd and the right is before.(bad focus).they are unprocessed except the modded has a slight red custom balance used and the moon was up as well...shows more blue after the modd I think....