Stopping down a scope advice needed.

[spaceboy]

Hi SGL members.

I decided to do some solar observing today with my refractor (Evo 120) and tend to use the 2" cap with solar film taped to the back. The view was amazing compared to my Explorer 200p when I do the same. Is this just due to the optics or am I missing something regards the stop down? Both telescopes are 1000mm Focal length and the smaller objective caps are 52mm. As the reflector no longer has a central obstruction as such and both f/ratios amount to F/19 I can only assume that glass works bet on our nearest star.

Looking for advice or similar experiences.

SPACEBOY

[chemtom24]

sorry this doesnt answer your post but ive always wondered why the top plastic cover of the telescope has 2 holes in it, both capped? is this so i can use a filter???? this would drastically cut the amount of light let in tho??

[spaceboy]

this would drastically cut the amount of light let in tho??

The sun is pretty bright

[chemtom24]

ah so is it purely for solar observing, to limit the amount of light that enters the tube? and can a filter be placed there as well for solar observing?

The sun is pretty bright

[Andrew*]

@ chemtom: For direct solar observing, an filter over the aperture is essential.

If you want to project the image of the sun through an eyepiece, stopping down the aperture is a good idea to prevent too much heat build-up on the secondary or the eyepiece.

@spaceboy: Excellent question, and the truth is I have no idea! Perhaps the thermals within the newtonian tube are deteriorating the view. Cheeky question: is the 200P collimation spot-on?

Andrew

[spaceboy]

The sun or moon when needed. Filter caps can be made or just tape Baader solar film on the inside with strong tape. The speed of the scope slows and you loose resolution but it cheaper than having a full aperture filter For serious solar observing there's no substitute for full aperture but in a 5-8" scope that's a lot of film to have to check for pinholes. With only a 2 1/2" circle of film if I'm not 100% happy with risking it I can chuck it and put a new piece on at no major expense. This is how I get over my fear of looking at the brightest thing in our solar system with out toasting my retinas.

[spaceboy]

@spaceboy: Excellent question, and the truth is I have no idea! Perhaps the thermals within the newtonian tube are deteriorating the view. Cheeky question: is the 200P collimation spot-on?

Andrew

It's collimated by laser standards but whether it would pass if checked with a Cheshire is debatable.

In truth I would have thought someone would have popped up with the answer buy now but I guess they are all avoiding getting in to another possible refractor, reflector debate. Either that or my thread title isn't explaining itself to well??

[Merlin66]

Pinholes in Baader Solar Film..... I've asked on another thread for honest feedback...Has anyone EVER found pinholes in a Baader filter?? The answer so far - NEVER!

Another urban myth???

[spaceboy]

Pinholes in Baader Solar Film..... I've asked on another thread for honest feedback...Has anyone EVER found pinholes in a Baader filter?? The answer so far - NEVER!

Another urban myth???

Sorry I missed this thread and just for your info I found one yesterday!!! So don't be negligent when checking and make sure you do check every time you use it as it only takes one miss and you could be regretting it for a long time. I agree due to the way Baader coat both sides of the film you often do get what looks like a pin hole but is actually a tiny miss in the coatings on one side and is safe to use because the other side of the film is coated to compensate. This said I had no doubt in my mind that this was a minute pinhole as it was visible from both sides when held up to the sun. Debatable if it was in the film from manufacture or done by me during installation but either way it's no big problem just put some tape over.

BETTER TO BE SAFE THAN SORRY!!!

[spaceboy]

Come on there must be some with suggestions. I know the refractor under normal circumstances is sharper and has more contrast on the moon but given this was solar observing and the offset of the objective on the reflector shouldn't the 2 scopes be on an equal par given there FL equal to the same, they both have unobstructed views and same aperture??????

Has anyone a better suggestion for a title or a better place to list the thread??

I know it doesn't make any real difference as I have the scopes at my disposal but it has aroused my curiosity.

[Merlin66]

The original post...There should be no or very little difference between the views. As you say, similar aperture, focal length, focal ratio.. The colour correction of the reflector is 100% but I'd assume the ED is pretty good.

The only other differences would be the local seeing conditions.

[spaceboy]

Thanks Merlin.

120ED I wish!!! unfortunately my Evo is only an achromatic. I do agree that refractors do offer better quality views over reflectors but just cannot compete when it comes to the important part of aperture. It just doesn't make any sense that when they were both placed on a level playing field that the refractor still showed improvements in image over the reflector. I can only assume it must be the collimation is worse than expected with the reflector????

[Peter Drew]

Don't forget that, although the optical parameters are the same in respect of your experiment, the light in the reflector option passes twice through the inevitably warmed air compared to the refractor's once, this can often make the difference.

[spaceboy]

Good point Peter. I thought as the focal lengths are the same and despite travelling the OTA twice it's only traveled the same distance through any thermals????? I understand what you mean and how this could be the cause.