a little help with the math please

[star_chaser]

hi all im having a little trouble with focus on the moon using my x2 barlow and i know that there is a math formula to work out max magnification you can use with a scope . now my app is 130 focal length 650 and web cam is the same as a 6mm ep i believe is this the reason for blurry image or me not being able to focus correctly ?.

also for others who have experience use the celestron 130eq any idea how i get around the problem of the locking nuts hitting the md housing when scope is pointing high up. the thing that you attach the cable to was hitting so i took this off(hoping it goes back on easily) and then the locking nut was hitting as i don't want to be just imaging low in the sky. this only happens when scope is at east axis (scope is on east side of mount counter weights on the west)not sure of the correct terminology

and lastly how much of an improvement would a 5"-6"(not sure of weight difference)i would like the 6" f8-f12 scope make when viewing imaging planets and the moon.

thanks in advance star

[Ursa Major]

What type of barlow have you got? mine is a cheap nasty skywatcher one where you need to screw the lens out a bit to be able to get focus.

[star_chaser]

its a revelation it came with my ep kit tho just looking at it there is/was a nasty big fingerprint on it looks like 1 question out of the way

thanks for getting me to check star

[Ursa Major]

Hopefully it will be better once cleaned. Just watch hove you clean it. There are quite a few tutorials on the internet.

Sorry, I don’t think i will be able to help on the other questions. hopefully someone more knowledgeable than me will be able to help.

[ollypenrice]

You can't talk about magnification in photography. You need to think in terms of 'image scale' or 'plate scale'. I would have thought a 2x Barlow should be OK in your scope, all being well. Ie you need to have the right back focus, the scope needs to be collimated, the camera needs to be square on to the light coming from the scope, etc.

Olly

[rowan46]

your maximum theoretical magnifification is about 40x -50x your apparture inch so say 250x tops your magnification is focal length divided by the eyepiece hence 630 divided by 6 equals 105. with a barlow x2 equals 210 your maximumum theoretical is based on perfect collimation perfect optics and perfect atmospheric conditions usually the seeing in britain isn't perfect so a telescope is rarely used at its max.

[star_chaser]

thanks for the tips and math lesson is back focus different to normal focus ???

and the camera being square say if the scope is at a 45 degree angle should the camera also be at 45 degrees or level with say the horizon

again thanks for taking time to answer

star

[ollypenrice]

By back focus we really just mean the distance between the focal point and the tube. Since the focuser has limited travel, particularly on a Newt, some lens/camera combinations lie outside or inside what can be allowed for in the focuser's travel.

Olly