ZiHao

Thanks. 35 lights and IIRC, 20 flats and no darks were taken. Generally people only take around 30 darks. I think you should try with maybe more/less darks or even without them to stack with your raws to see how much it helps the image.

So I am planning to make a dew heater for my camera len using resistors wired in parallel, then distributing them around the circumference of the lens. Diameter of lens: 65mm Total power output: 6W Power Supply(powerbank): 5V, 2A, 20Ah Resistance for each resistor: 120 Ohm Resistor power rating: 0.25W Power output for each resistor: 0.21W Current drawn: 1.21A Number of resistor required: 29 Will probably insulate the wire with tape, and wrap the resistors in cloth around the lens. Is 6W too much or sufficient for this use? Any suggestions? Thanks.

Hi, Yesterday a partial solar eclipse happened here so I took a few pictures using a DIY solar filter with the provided dust cap. And the center seems to have a blurry circle or reflection. Any idea? I don't remember this happening to the image when I use a full aperture filter which I wasn't using this time, was worried that it may fall off. Thanks.

Shot with SW150/750, ASI120MC and 2x Barlow. Stacked on AutoStakkert!, edited on Registax and PS. Hold your phone away from you, it will look better😅

Tried it, doesn't work. I selected the ZWO USBST4, the slew buttons just don't work. In PHD2 Manual Guide everything is okay as the option 'On Camera' is available. I guess EQDIRECT cable is necessary then.

I have seen a lot of questions about this topic but didn't get a clear answer. Is there a way that I can dither without guiding using APT and PHD2? I am using ST4 cable now and mounting a DSLR + kit lens on my EQ3 Pro to do normal sidereal tracking (maybe dithering is redundant at short focal length, say 24mm?) Will disabling the RA and DEC corrections in PHD2 still allow dithering? Because I don't need guiding for the widefield setup and not planning to mount the guidescope on top either. Thanks in advance.

Stars seem to 'travel' faster on the celestial equator than the stars situated at the poles. Why is this? Is this just a perspective problem?

I think if you want to avoid light pollution, travel to Mersing which I believe is close to your location.

Anyone done astrophotography with this guidescope? Sounds like a stupid idea, but being limited on budget, I was hoping to mount this on my EQ3 pro instead of the heavy Newtonian reflector. It costs only 120 dollars, a really cheap refractor. What do you think?

I am using a DSLR and only takes bias frames and flat frames but no darks as the temperature I believe doesn't match. I heard that if you already have bias frames or when the flats are of short exposures, you don't need dark flats. But IMO, usually dark flats aren't necessary. What do you think?

Thanks for suggesting! I will try that later.

Thanks! Skywatcher 150p with ASI120MC and 2x Barlow.

Stacked on AutoStakkert! and sharpened on Registax and PS. I wish I have access to a longer focal length to photograph this wonderful planet😁.

Ah, I think I misunderstood the term "faster" here, I related it to the light gathering ability of the camera, light gathering ability as in like, for example, we have one deep sky object that both the sensor can capture completely, now we crop it to the same size so both images show the same features of the DSO, so the SNR for both of them will be the same, therefore for different sensor size using the same focal ratio scope, how fast they collect light is the same. I agree the larger sensor covers wider FOV whereas smaller sensor covers smaller FOV and larger sensor is faster, in another way, that they will cover bigger area of the sky and the total light collected will be greater. Thanks for clarifying, I hope that I didn't confuse myself again.

Using the same scope but with two different sensors size, why would the combination with bigger sensor be faster when they have the same focal ratio? Please correct me if I misunderstood this.

Thanks for writing the summary, Steve. I will have a look at the book. Looking forward to your zoom meeting later at 3am as well 😁

Hello all, Any good books or websites out there about theories of astrophotography? Things such as SNR, types of noise... would be great.

Hello all, Recently I have been thinking to implement dithering to my mount to remove walking noise, but my mount has a declination backlash, around 3 seconds or less. So is it okay to disable the dec guiding, and let APT and PHD2 dither in RA? I have heard that this will introduce more noise to my DSLR images. Another solution is to try measuring backlash in guiding assistant and guide in both dec directions, will it give good dither results under backlash compensation in PHD2? What do you think?

In manual focus, the focus ring might shift a bit when I am shooting widefield images and taking flat frames, is there a way to lock the focus ring? Thanks.

35 x 1 minute of Lagoon Nebula under Bortle 8 skies taken with stock D5300, SW150/750 and EQ3 Pro. Had to say the gradient in the image was really bad because of the lazy and forgetful me that took the flats in a different camera orientation plus the possibilities of light leaking into the setup. Thanks to @alacant for giving the advice on stacking and AstroBackyard's Astrophotography Tutorial: How to Remove Gradients in Photoshop. Although the way of removing the gradient seems extremely unusual to me, but it works! I believe a lot of the advanced softwares like Pixinsight or plugins such as GradientXTerminator would solve the problem very easily.

Alright, took 50 bias frames just now and got this. I just won't learn from my mistakes lol, I took the flats with a slightly different camera orientation as I removed it before the next session... This is probably why the image has a linear gradient across I think. The overall gradient looks slightly better compared to the ones uncalibrated and with flats only, in my opinion. Yep, this is a Skywatcher 150p. I just loaded all the bias and flat frames into DSS and let it do its job. I think that's ok too? Great idea! I will get a shower cap then. Thanks a lot. biasflatm6.TIF

Hello all, here to ask about uneven field vignetting and whether it is caused by collimation or not. Attached are pictures of a single raw flat, then the same flat applied with contrast adjustment, telescope's collimation, lagoon nebula stacked of 37x1 minute subs consisting of just light frames. I found that the coma in the field has been getting worse that they started showing so early, close to the center of the image. I was wondering whether this is normal or just because of my bad collimation, but collimation looks fine in the attached picture with everything centered. And the flat as well, it looks darker on the left side, I think this might be due to camera or adapters tilting a bit, or even collimation again? I thought about light leak in the scope, but it does not seem be the problem. But still, I did some light leak test because of the unending, annoying gradient in the picture, by shining my phone's flashlight on the primary mirror, and there's light leak! So in the next imaging session I will try to cover the mirror and also my DSLR's viewfinder as I am imaging near a streetlight. I have also heard that without bias frames, flat frames wouldn't work well when calibrated to the lights. Thanks in advance and clear skies.

I thought EQMOD only works when you have a EQDirect cable? I have been selecting 'None' in the previous sessions. So I have to install EQMOD as well right? The ASCOM drivers are installed as I am using ASI120MC to guide.

I am currently using a ST4 cable to guide, so do I need to select anything under the Aux Mount selections? There is a 'ZWO USBST4 ASCOM' option.

Just to confirm, when shooting from APT, I always close the flipping screen of the camera. Is this the correct way? Sorry for using this thread.