My 100mm F5 Acro refractor is not very good for astrophotography because of the huge blue halos around anything bright. But I thought I'd try some photography using my Baader Semi Apo and Orion V block filters. They actually did make a much bigger difference photographically than they do visually. I screwed the V Block filter (which seemed to control the CA a little better than the Semi-Apo) into the end of an eyepiece, then removed the silver barrel section of the eyepiece so it could slide inside the 2" to 1 1/4" reducer that my camera fits to. This is a single 99 sec exposure iso 1600 unguided on an HEQ5 mount. (Pentax K50) There was some noise reduction and CA processing in Lightroom along with some exposure/contrast/vignetting adjusting. There's still some CA evident but it's way better than an unfiltered shot. I know it's not very sharp but one day I will get an autoguider and appropriate mount to suit which will help immensely. One other problem I became aware of is that any bright objects seemed to reflect off the V block filter back onto the sensor producing some nice big purple circular artifacts - oh well, rob Peter, pay Paul!
Well done mate!
It's a creditable image, shows potential.
Re filter ghosts - a couple of things to consider - a CPL filter does a good job of suppressing unwanted reflections, also a slight tilt to the filter element can throw the ghost out of the FOV.
Cheers guys. Ken, I'm not sure if I can tilt the lens but it did make me think that if I move the V blocker away from the sensor an inch or so, it may lessen and spread out the reflections. Worth a shot.
Polar alignment is just done squinting through the polar scope and trying to hold a red torch over the opening in the mount so I can see where Octans is suppose to be. I must try the DARV drift alignment test next time. I can definitely see image shift between exposures - not sure if that's just par for the course with the HEQ5 or the alignment could be better.
Just for fun, here's a 30 second shot of the Pleiades without a filter, and the same shot with the Orion V block in place - you can start to see the filter reflections, but the filter does a pretty respectable job in getting rid of those blue halos. I've stretched these in PS to highlight the details but no other processing.
With your rough and ready method of polar alignment, and 500mm
optics, it would be par for the course with any mount. I don't know what
you mean by an appropriate mount; a properly aligned HEQ5 will do everything asked of it by a beginning or intermediate level imager.
Many imagers use their HEQ5s and/or NEQ6s happily for years.
raymo
With your rough and ready method of polar alignment, and 500mm
optics, it would be par for the course with any mount. I don't know what
you mean by an appropriate mount; a properly aligned HEQ5 will do everything asked of it by a beginning or intermediate level imager.
Many imagers use their HEQ5s and/or NEQ6s happily for years.
raymo
By 'appropriate' I meant one with an autoguider port which mine doesn't have - at least I'm under the impression that I cannot use an autoguider without modfications so I'm stuck with relatively short exposures or manual guiding. I'll give the DARV method a try next time and see if I can refine things a little
It just occurred to me that you might have an HEQ5 not an HEQ5 ProGoto.
Does it have a Synscan hand controller, or just a motor speed hand controller? You don't see many HEQ5s, so I presumed that it was the
GOTO version. All HEQ5 GOTOs connect to an autoguider through the
ST4 port to the right of the power on/off switch.
DARV is relatively quick, and easy after a few goes.
Manual guiding in these days of dozens, scores, or even hundreds of exposures for one image
is for the birds. Fine back in the days of film.
raymo
Last edited by raymo; 30-10-2017 at 01:51 AM.
Reason: more text
It just has the motor speed hand controller - no goto or ST4 port. Hey, does that make it a No-Go mount? I think I looked into modding it several years ago but decided the risk of fubar was a bit much!
I think you'd be better off selling it and buying a used one from the classifieds here. Being very popular they frequently come up around $700-800. I think
the cost of modifying yours would be more than that.
raymo
The stars in the center seem nice and round to me yet to the edges they are a little oval which points to perhaps issues other than guiding.
Anyways great effort.
alex
Thanks Alex. Yes, only about the center 3rd of the frame is reasonably sharp with this lens. (I'm using the term 'sharp' pretty loosely here!!) It's quite obvious with daylight shots too. Still, for a $300 telescope and UV filter I am pleasantly surprised. Without the filter, it's a different story!
I have 400mm achro refractor, and i am modifying it a lot, first i am changing the focuser to 2" Crayford i hope, then i am buying a universal or whatever flattener [for F5 up to F8] to solve the field curvature, and then i shoot with an astro mono cooled camera and filters, so it is like 60-80% of achro issues are gone or covered or minimized, i do all that to save myself from buy an APO triplet expensive telescope, so i can buy a visual planet scope first [SCT maybe] while i can enjoy with my modified ST80 for DSO AP.
If this will give me nice results then i will definitely buy another Achro telescope with 600mm or longer, so with the price of good APO i can have 2 or 3 achro telescopes and modify them.
If this will give me nice results then i will definitely buy another Achro telescope with 600mm or longer, so with the price of good APO i can have 2 or 3 achro telescopes and modify them.
I think if you already have a relatively cheap acromat refractor, A UV blocking filter can vastly improve performance. But I'm not sure that I would buy one for astrophotography. The ED80 is an excellent scope - much nicer than the 100mm F5 acro, and the ED80's come up second hand for very reasonable prices. The ED100 F9 is also very sharp on planets - perhaps a bit slow for photography. If you are after something around 600mm, keep an eye out for a s/h ED80. They're very good value for money.
I think if you already have a relatively cheap acromat refractor, A UV blocking filter can vastly improve performance. But I'm not sure that I would buy one for astrophotography. The ED80 is an excellent scope - much nicer than the 100mm F5 acro, and the ED80's come up second hand for very reasonable prices. The ED100 F9 is also very sharp on planets - perhaps a bit slow for photography. If you are after something around 600mm, keep an eye out for a s/h ED80. They're very good value for money.
I have Contrast boost filter that kill that CA completely, so i don't need to worry much, the side effect is getting a warmer color, so it is up to people if they want normal color with CA or free CA but yellowish a bit overall color.
Also, i will buy an APO triplet scope later in the future, i will save for that, i just hold on my current achro fast scope until i can afford something better, and i did say that i have a mono camera, so i don't have too much issues after all, but i am soon will buy LRGB filters and i will see if i will see CA too, some told me i will see that with blue filter, so i have an idea in my head if that will happen.
My V-block filter (which I think is pretty similar to your contrast booster) can give a yellow/green tinge to photos - but that's not hard to correct in Photoshop. I will be interested to see your photos in the future.
My V-block filter (which I think is pretty similar to your contrast booster) can give a yellow/green tinge to photos - but that's not hard to correct in Photoshop. I will be interested to see your photos in the future.
I was thinking to get that Semi-APO filter too, but i decided i will give narrowbanding and LRGB that i will buy soon i hope more try later and see what kind of issue i may face, then i can decide if i should buy more filters or not, but i really not looking for to have amazing errors-free images yet, all what i care about is to get photos of targets first with or without issues then i will think about solving issues one by one, including a color tint.
Tareq,
Imaging with blue filters shouldn't be any more of an issue than with the others. You will have to refocus for the blue end of the spectrum.
I don't understand this point, the filters i am buying are Parfocal, and the seller told me that the focus will be fine for each filter, but let's see when i will get the filters, but if you think that each filter will give me fine results without problems then i should be happy, i really don't care much about CA itself, and i didn't see anyone tried with an expensive mono astro cooled camera with very cheap achro scope/guide such ST80.
