Should I remove the hood from my refractor?

[Och_Aye]

First post!

I have a Skywatcher 90 Evostar refractor, which has a large hood.  The cap in the hood has a diameter of c. 60mm so surely I'm losing a huge proportion of the available light?  I can slide the hood forwards to reveal some screws but aren't comfortable with the idea of taking them out, if the hood was meant to come out with normal scope use, then surely the design would've taken that into account?

Am I actually losing any light?  Is there anything I can do to improve the performance - don't get me wrong I love it but if I'm missing a trick then I'd like to know

cheers

[Dave Lloyd]

Welcome to sgl. Not sure what you mean, if it's the full width cap on the dewshield, that comes off. The centre comes out separately. You have the full 90 mm aperture with this scope.

[Putaendo Patrick]

I'm a little confused by your terms, so I wouldn't want to recommend anything that you misinterpret.

Check the photo at FLO, and tell me if this is the full aperture you have:

http://www.firstlightoptics.com/evostar/skywatcher-evostar-90-eq3-2.html

If not you are effectively only removing the central part of the lens cap. If you can open this photo, you will see the difference:

http://img1.kapaza.be/desktop_images/32/323524097878039.jpg

Otherwise if you are refering to the "extra tube" which extends out from the lens, this is designed to prevent or reduce the formation of dew on the lens.

[MarsG76]

60mm hood on a 90 mm objective refractor?? that doesnt sound right.... perhaps replace it with a bigger hood. I suspect that buy removing your hood, you will have more issues with dew accumulating on your lens.

Although looking at pictures of it, it seems to look right.

[MarsG76]

hang on.. are you just removing the center part of your lens cap??? if so, then you need to take off the whole cap to reveal the whole objective... if you're only removing the center cap off your lens cap and leaving the rest on, than yes, you're crippling the light gathering, and therefore quality of your telescopes performance.

See the picture attached, you would need to remove the whole thing, whole black cap, not just the middle bit.

By the way, Welcome to SGL.

[Och_Aye]

Cheers ... and I'm feeling very sheepish right now!!! Yes, I had only been removing the centre cap, now I just need to wait for the rain to clear to see what the scope can really do!!

[MarsG76]

It'll be like having a new scope all over again... Like a upgrade in size and the best part, it's free... 

[Charic]

You wont be the last, others are fooled by a similar cap on the Skyliner?

Don't feel any guilt or shame, just laugh it off.

Dark  skies to you

[brantuk]

Don't undo any screws unless you know exactly what they are for. You could end up wrecking the collimation of your scope and it would need an expert to redo it for you. Keep the hood in any event - it helps reduce light intrusion from light polluted areas and helps to keep the dew off the front objective lens. Hth

If it's just the front cap then take it off by all means - you won't see anything with it on.

[Putaendo Patrick]

There's a good review of your telescope by Alkaid here:

http://stargazerslounge.com/topic/141556-skywatcher-evostar-90mm-refractor-review/

One of his photos shows the lens end with cap removed. Hopefully this is what you now have!

Clear skies - although Murphy's Law always determines days of cloud/rain/fog etc. when you first get a telescope!

[ronin]

Learn something at times you least expect - an Evostar 90 has a central cap/cover, that was something I never knew, or even considered.

You may say you feel sheepish but I for one never realised they had such a construction.

At 90mm diamter the primary thought is Why?.

Not relevant to a solar filter as you get a full aperture for that, and 90mm is good for everything you are likely to go looking at.

Bet it reduced dew forming on the primary at least , and I guess the increase in aperture will be an improvement.   Guess M42, Orion Nebula, will look a bit different.

[LukeSkywatcher]

I spent about 6 months looking through my 90mm scope.........through the central hole. I wondered why images looked so dark. Then i discovered the whole dust cap could and should be removed.

The "hood" is a dew shield which extends out past the lens. This should be left on the scope. Dont take out the screws underneath because these hold the lens in place.