Bahtinov mask help.

[leelee970]

Is there an optimum distance to use this type of mask.

The reason I ask is that I’ve a foam dew shield on my scope which is a little tight to remove.

At present I use my home made cardboard mask and carefully place it down the dew shield until it rests on the end of the scope and therefore close to the secondary mirror.

Could it be used at the top of the dew shield and still give me excellent focus?

If so I’ll invest in a better Bahtinov mask as the cardboard one has seen better days.

Many thanks for any help.

Lee

[Velvet]

I was always told to put it directly on the end of the OTA, I am unsure of it on the dew sheild as that would make

the tube longer than it should be for the scope, although i cannot think of a reason why you cant try it . I am sure someone else will correct me if i am in error

Velvet

[tingting44]

seeing as they sell the masks for actual sizes of telescope i'd say that your focus would be out if putting it on your dew shield mate, you need to use these on the end of the actual telescope

[foundaplanet]

I may get corrected here but I believe it makes no difference placing the mask on the dew shield.

[todd8137]

seeing as they sell the masks for actual sizes of telescope i'd say that your focus would be out if putting it on your dew shield mate, you need to use these on the end of the actual telescope

That's a little wrong

[todd8137]

I image all he time ,now I never take my dew shield of to use a mask ,if you have no dew shield it's got to go on the end of he scope ,if you have a dew shield ,then stick it over the end

if you do not image and still want focus to be great then just stick on the dew shield.

Pat

[tingting44]

That's a little wrong

please explain as im far from an expert lol why do they bother selling the masks for different focal lengths then? surely they would just make one mask for all if it were possible?

http://www.firstligh...ocus-masks.html

Premium quality Bahtinov focus mask.

These are not generic masks, each mask is tuned to the telescope's focal ratio for the very best performance.

[perkil8r]

They are designed to go on the end of the dew sheild, hence the size and also the placement of the pegs or screws.

[perkil8r]

please explain as im far from an expert lol why do they bother selling the masks for different focal lengths then? surely they would just make one mask for all if it were possible?

http://www.firstligh...ocus-masks.html

It IS possible to make a focus mask to fit all scopes, but it's not the same sort. The masks are designed for a particular scope, that scope will have a particular dew sheild if it is a frac. In which case it stays on. If you're using a newt, then yes, remove anything that's not as manufactured such as aftermarket dew sheild, that goes without saying. As a rule, use the mask directly over the end of however the scope comes as supplied by the manufacturer. In the case of a frac that does not mean remove the dew sheild.

[JKB]

Always use my B-Mask on the end of the Dew Shield. Doesnt make a difference as far as I know. Focal length of tube is the same and all the mask does if cause diffraction of the incoming rays?

Also use Bahtinov Grabber software to double check (Well when I have time!!)

Cheers

Jamie

[madatter]

what about a Skywatcher 130m at 900mm and the 130p at 650mm both use the same mask.