diy Baader solar filter for 8" Dob - Full aperture/quarter?
Hope i'm posting in the right forum
I bought an A4 size Baader AstroSolar film off Ebay to make a solar filter for my 8" Dob, I've done my search on the subject and I've seen different pictures of people only using a quarter of their aperture, but there are products for 8" SCT that filters the whole 8"'s worth.
The big question is what would I expect from (or should I even consider) a full aperture filter compared to just a opening a quarter (á la the duct tape filter on sidewalk astronomer's website) or even something in between?
Hi Nathan, The main difference between a full apeture filter and one that is reduced as you mentioned, say 1/4; then this effects the amount of light entering, therefore a smaller apeture (similar to a camera lens ) will need a longer exposure, thus picking up more atmospheric turbulance ?
Hope this helps
I have a 1/4 offset solar filter and even with this the amount of light coming through is almost exceeding my shutter speed on my DSLR. My webcam required numerous filter to turn the level down. I would expect the same result will happen in yours. Mine essentially is pulled down to 3" aperture.
I haven't ventured into AP yet! I was just wondering the difference for my eyes. should have clarified that I was lead to think higher aperture would mean greater detail if I want to view the sun(spots) at higher power, but as a lot of you have done, 3/4 of the telescope is covered so I'm just wondering why (and why not full aperture).
Try both and see. Given you are not trying to collect light, but rather reject 99.99% or so of it, the only issue is the resulting resolution performance.
There is another thought. Using a 1/4 circle, you can position the filter to entirely avoid the spider vanes which I do with my 8" Thousand Oaks 1/4 solar filter. Perhaps that is a good thing to do?
I'm putting the filter together this arvo. I'm still curious as to why any effort has to put in to avoid the spider vanes (perhaps to save unused filter?) and there's no concrete reason as to why I can't use a full aperture for viewing. However that said, I'm stopping the 8" down to 3-4 inches just to err on the side of caution, since all DIY ones are done this way for whatever mysterious reason. will post pics.
P.S. any cheap places to buy (double/mounting/duct..) tape? officeworks is quite expensive!
I should say, Nathan, If I had a full 8" I'd happily use that rather than a quarter aperture. I picked up the quarter cheaply from someone who lost interest after the last Venus transit, I would never have justified the price of a full aperture glass filter.
It just seems that, if you have a quarter, then why not avoid the spider vanes. Probabaly, the improvement on the Sun of avoiding a spider vane would be miniscule. I just don't know.
ahhh Eric you will just keep me wondering what a full sized aperture would look like compared to a 1/4 one (as I did have enough film for a full one...)
There was definately a lot of light coming through. Even with the ~3" aperture I felt slightly uncomfortable and used a moon filter (point and shoot took in a looooot of light too). Trouble was things didn't focus quite well at mid to high power. Would it be due to turbulance (or other atmospheric reasons) or the aperture too small (calling for an full 8" filter for better magnificaitons?) and things looking fuzzy and dim when when viewing in high power?
no proper AP involved.
Last edited by clarinetcola; 01-02-2012 at 11:52 PM.
Reason: ...
I bought an A4 size Baader AstroSolar film off Ebay to make a solar filter for my 8" Dob, I've done my search on the subject and I've seen different pictures of people only using a quarter of their aperture, but there are products for 8" SCT that filters the whole 8"'s worth.
The big question is what would I expect from (or should I even consider) a full aperture filter compared to just a opening a quarter (á la the duct tape filter on sidewalk astronomer's website) or even something in between?
cheers!
N
I'm planning to do the same thing for my 10". Why not make it full aperture but also make a mask or two with different size apertures to fit over the full aperture.
From memory in using other members dedicated solar scopes at Snake Valley this type of filter shows you the sun spots but cancels out the prominence. Is this correct?
Just use the aperture reduction hole on the dust cap of the scope. It is around 2" in diameter. Just tape the film over that. It's more than enough.
If you make a full aperture filter, you will end up with a big floppy piece of film over the front of your scope, there is more chance of it sagging, flapping in the breeze and the tape pulling and coming apart. Resulting in instant blindness to the observer or a fried sensor on your camera.
It's one of the very few times in Astronomy that less is more.
As proof, this image was taken through an 80mm scope , stopped down to 50mm. The film was taped over the hole in the dust cap.
The camera was set at ISO100, exposure time 1/750th of a second.
The lid off the can of spray paint or similar is almost exactly the right size to slip over a standard 50mm finder scope. Cut a 20mm hole in the end, and tape down the film to the inside using dbl sided tape and reinforce with regular tape.
Just use the aperture reduction hole on the dust cap of the scope. It is around 2" in diameter. Just tape the film over that. It's more than enough.
If you make a full aperture filter, you will end up with a big floppy piece of film over the front of your scope, there is more chance of it sagging, flapping in the breeze and the tape pulling and coming apart. Resulting in instant blindness to the observer or a fried sensor on your camera.
It's one of the very few times in Astronomy that less is more.
As proof, this image was taken through an 80mm scope , stopped down to 50mm. The film was taped over the hole in the dust cap.
The camera was set at ISO100, exposure time 1/750th of a second.
The lid off the can of spray paint or similar is almost exactly the right size to slip over a standard 50mm finder scope. Cut a 20mm hole in the end, and tape down the film to the inside using dbl sided tape and reinforce with regular tape.
Bump - Resurrecting an old thread....
Hi JJJ (and anyone else who can offer advice),
I would like to use my 12" Sky Watcher Collapsible GoTo Dob to view the Venus Transit in June. I wish to use the method quoted above to safely view the Sun. The plastic dust cover on the 12" Dob has two off axis 50mm Dia holes, one with a removable cap.
If I purchase some solar film and fix it over the 50mm dia dust cover hole, will I be able to achieve the same level of viewing quality as JJJ's 80mm scope has in the image attached to the last post?
Thanks.
Last edited by Shark Bait; 14-03-2012 at 08:39 PM.
Stu, I strongly recommend that, for a truss or strut reflector, you have a shroud in place unless you are absolutely confident that sunlight cannot come onto the primary when you move the scope so that the Sun is off axis. If enough hits the primary, it may well be concentrated to sufficient focus to burn something.
"Another hazard for an open truss tube, with no shroud, is created when a person stands next to the telescope. I walked by the scope and received a huge blast of sunlight in one eye (fortunately it was too brief to cause damage). Even when the light is far off axis, the mirror can be a powerful solar concentrator."
Stu, I strongly recommend that, for a truss or strut reflector, you have a shroud in place unless you are absolutely confident that sunlight cannot come onto the primary when you move the scope so that the Sun is off axis. If enough hits the primary, it may well be concentrated to sufficient focus to burn something.
Thanks Erick,
I should have mentioned that I have made a shroud for my scope. I have attached an image of my scope with the shroud in place.
The damage caused in the photo you posted is my main concern. I would not be able to forgive myself if i turned someone's eye into jelly. Interesting thread from cloudy nights, even the seasoned observers get caught out.
I am still keen to get some solar film and try to observe Sol.
Even with a shroud in place, I am still concerned about the safety side of viewing our Sun.
Should I still try this using my scope with shroud in place?
Your dust cover lid bit thingy also fits the very top of your scope too.
Covering the offset aperture reduction hole with solar film is still the go.
No unfiltered sunlight will be entering the tube.
Don't forget to make a filter for your finder. .
And use a shroud to stop stray sunlight bouncing off mirror by accident.
Your dust cover lid bit thingy also fits the very top of your scope too.
Covering the offset aperture reduction hole with solar film is still the go.
No unfiltered sunlight will be entering the tube.
Don't forget to make a filter for your finder. .
And use a shroud to stop stray sunlight bouncing off mirror by accident.
I have made my Solar filter cover to the size of the off axis aperture hole which has the additional benefit of having the same diameter as the finderscope.
This way, I keep the cap on the finderscope, use the 50mm cap on the main scope and if I need to adjust position with the finder, cap the main scope, stand in front of it so the scope is in shadow, swap the filter to the finder and then align, rinse and repeat....
Less to make up but obviously a larger risk overall if you are not careful.
User beware, but may save time and effort. ( I did this mainly because my baader filter is all used up.... and I am too cheap to buy some more)
I was lead to think higher aperture would mean greater detail if I want to view the sun(spots) at higher power, but as a lot of you have done, 3/4 of the telescope is covered so I'm just wondering why (and why not full aperture).
(as I did have enough film for a full one...)
