alacant

None. It serves only to liken terrestrial photography with astrophotography, which is both confusing and largely useless. The reducer makes it like a zoom lens. Maybe you have seen lenses such as 75-300mm f4.5-5.6? The OP has a telescope of 73mm diameter with or without a reducer. He is changing the f-ratio by altering the focal length rather than the aperture. The zoom lens is this example changes both. The OP's telescope, focal length only. Non reduced: 430/73 = f5.9 Reduced: 344/73 = f4.7 Both collect the same amount of light. But it gets even worse. As @david_taurus83 explains, the image may be brighter at f4.7 Cheers

Hi Remember to look at the images rather than the numbers, but anyway... Lose the external autopec and instead guide RA using PHD2's PPEC with an initial period of 480s. If not, as per @kens' request. Cheers

https://a.aliexpress.com/_uHxrd1

I've only tried a zoom once; a 75-300mm which came as part of the 700d bundle. It's ok as a daytime lens but no good for astrophotography. Well, not with me in charge of it that is. We've just posted an example with a fixed 135mm lens. They can be picked up cheaply and I can recommend this as a possible route into what you want to achieve. It also makes your apt profiles manageable. HTH

No. The maximum opening of the lens. This corresponds to the minimum clear diameter of the lens cell along the light path. In this case 12.2mm. if it helps, look through a lens as you zoom. You'll see the aperture change as the focal length changes. At 200mm, the aperture is larger so as to keep the f-ratio at f4.5. In fact some zoom lenses can't manage to keep the f-ratio the same and can quite often offer a smaller ratio for the longer focal lengths. E.g. 55-300mm f4.5-5.6. HTH

No, not due to the blades as they will be fully open. At 55mm, 12.2mm is the maximum opening.

Hi and thanks for your comment. Yes, it's a modified 700d. Good luck with the Pentax. Just take your time and I'm certain it will go smoothly. The Zeiss 135 certainly delivers on definition.

A typical (affordable?) 55-200 zoom has a maximum f-ratio of 4.5. Maths: 55/4.5 = 12.2 But don't let that put you off. Many of us put up with it. Worse, even; you'll have to close the aperture even smaller to get decent stars. Frightening eh?! Cheers

Short version: your lens has a focal length of 55mm. Enter that value in PointCraft instead of your current telescope focal length.

Hi Yeah, it's the same as using a telescope. Just enter the focal length. But bear in mind that a typical zoom lens at 55mm (to fit in the whole of Orion) has an aperture of only 12mm; painfully slow. Which probably explains why 12mm f4.5 refractors never caught on! Cheers

No need to wait. A well known Chinese based outlet;) Ask for European shipping at the checkout. Make sure you are ordering from the manufacturer. If the store sells jigsaw puzzles, sunglasses and wine cooler sleeves as well as step down rings, look elsewhere!

Hi. 135mm. Thanks for examining.

Ah, Siril. A much better choice:) You need a linear image; a stretched image from a dslr will not calibrate either. Just use the colour calibration:

Hi everyone Very windy last night so no go, even with a small telescope. An old lens on some heavy dovetails however, provided some resistance to the irregular gusts. A UHC filter seems to have helped with the usual taken-with-a-cheap-old-lens appearance and the -erm- aperture mask worked wonders on the star spikes. On the downside, there are a few reflections from the brighter stars, although easily 'healed' in StarTools. Anyone else tried the UHC? Problems with reflections? Thanks for looking. zeiss 135 mc-s on 700d @ ISO800 ~ 2 hours

Hi easy: Select only the outer regions for stretching. better: Make 2 layers with the a stretched layer over a non-stretched layer. Mask the top layer. Then, using a fuzzy brush, erase the mask where it's over-done. best: move away from the 1990's stretch/layer/hope-for-the-best stuff. Try contemporary algorithms instead. After you've been moving sliders around on a graph for a few hours, destroying it's linearity from the word go, StarTools comes as a breath of fresh air. I'll leave the building right away. HTH

Hi If you arrive at f4.8 by increasing the aperture, then yes. All you have done is reduce the focal length, so the amount of light collected is the same. The only benefit will be as outlined by @geordie85. If you don't need the reducer to also flatten the field, I'd stay as you are. Cheers

Hi. Well done on the image. Siril is here. HTH

Exactly, so where you were starting from was NOT the home position: you've lost the correct mount home. If you are starting from the home position and you request 'goto home position', the mount should not move. Set the home position as I described above and that should do it. Home position: DEC 90°. Counterweights down and telescope aimed at the pole.

Sorry, I'm thinking INDI. Park in asiair is called 'goto home position'. Cheers

Hi Loosen the clutches and park the mount. Now set the home position and tighten the clutches. Any good? HTH

Hi We use both the Zeiss 135 and the Takumar 135, the latter just having the edge. But as @Alien 13 points out, both are no go on a Nikon body. Bear in mind though that old lenses give nothing like their modern (and more expensive) counterparts' quality and fall a long way short of an imaging telescope. HTH

Join an astro club or contact locals who are already on the road to bankruptcy, see the equipment you need, how to use it and so always have someone on hand to tell you what you've done wrong when it doesn't work. No amount of reading is gonna get you anywhere near hands on;) And @bobro's recommendation notwithstanding, that's advice from someone who is already in Spain! Cheers

Hi I used to believe that aperture was the key to this and that the greater the aperture, the brighter. But in fact it isn't: f5 is indeed brighter than f10. Thanks to @vlaiv for explaining this. To answer your question, I'd say the galaxies would appear smaller, but brighter. Cheers

But you now have a super bright and reliable astrograph. Would you agree it was worth it? No need to answer. That image in just 60 minutes says it all! That's an interesting point; where and under what ambient lighting was the processing performed? If you did it in a room with subdued lighting, the chances are that it will emerge dark and vica versa. Indeed, it's difficult impossible to cater for a web audience viewing a .jpg on myriad un-calibrated devices and just as many different ambiences. Excellent job in both hardware and software and good on you for sticking at it:)

Hi A DSLR reaches focus easily with a pds. Could you post a shot of the camera attached to the focuser and tell us how you are viewing the focus e.g. through the viewfinder on the camera or via an app? Otherwise, we're guessing. Cheers