Astrophotography - Ektar 100 vs Portra 160

I am starting to get into astrophotography.

I am making big RA4 prints, about 40x60cm. In near future, I plan to make even larger prints.

I have already tried with Portra 800 the Moon and the Sun. Also, next summer here in Spain there is going to be a solar eclipse.

My goal is to get the finest grain and the hightest resolution/sharpness film.

I have tried Portra 160 few times and, some photos looked like digital - very fine grain and great sharpness. That´s is what I want.

Portra 400 and 800, and Black and White films are discarded.

I have heard too that Ektar 100, yes,It has very fine grain, but it lack of resolution. True or false?

So, is Ektar 100 going to be better on terms of grain, resolution, sharpness and acutance against Portra 160?

I would like to hear from people that made prints (RA4 preferably) with these film and their opinion. Also, I love technical information.

Let´s talk about the film stock that we have today - the possibilities in 2025.

I started with jase.film (https://www.instagram.com/jase.film/?hl=es) (https://www.jasondefreitas.com/)

You know...monkey see, monkey do.

I wouldn't sweat it that much. One millimeter squares.

Portra 160



Ektar 100

You may see slightly higher acutance with Portra160, but resolution on both should be fine. Will you be printing from 35mm or larger negatives? This evidently will make a lot of difference.
I find it's difficult to get crispness (high acutance) on large prints from 35mm color negative. Digital works better for me for that purpose.

What is your setup for avoiding motion blur during the required long exposures? Just curious!

arturo_rs said:

I started with jase.film (https://www.instagram.com/jase.film/?hl=es) (https://www.jasondefreitas.com/)

You know...monkey see, monkey do.

Click to expand...

Thanks for sharing! OT, but I just love the video where he puts a super 8 camera on an FPV drone.

Good luck with your project!

koraks said:

You may see slightly higher acutance with Portra160, but resolution on both should be fine. Will you be printing from 35mm or larger negatives? This evidently will make a lot of difference.
I find it's difficult to get crispness (high acutance) on large prints from 35mm color negative. Digital works better for me for that purpose.

What is your setup for avoiding motion blur during the required long exposures? Just curious!

Click to expand...

I use 35mm, 3 cameras (Nikon F100, F70 and F301. The lenses:

Nikon AF-S VR 70-300mm F4.5-5.6G
Nikon 50mm F1.8 D

For the sun I use the Baader Sun filter ND3.8. To see the sun with my own eyes, the filter ND5.

For long exposures:

1-Tripod
2-Motorized equatorial mount - SkyWatcher-Star Adventurer
3-Guiding tube ZWO 30mmF5 Mini
4-Camera for the guiding tube: ZWO ASI120MM

The software (both free):

Open PHD Guiding
Cartes du ciel (it shows what are the star in a specific location. Just orientation).

A laptop too.

​

Once config the equatorial mount using the polar star, you have to track one star using the camera zwo mounted with the guiding tube. Using the software, it makes calculations and move the equatorial mount.

I think the choice between Ektar 100 and Portra 160 should be determined by the desire for color saturation, reciprocity failure, and difference in film speed.

Portra has worse reciprocity failure but it may not matter to you depending on how long these exposures are. At 1 minute measured, Portra goes to 4 minutes. Ektar goes to 1 minute 40 seconds. It's a big difference.

At some point if you go to a long enough exposure, Portra 160 and Ektar 100 would have equal exposure times. This happens around 10 minutes in the real world. Because a 2 minute measured Portra 160 exposure is 10 minutes and a 3 minute measured Ektar 100 exposure is also 10 minutes. After the 10 minute mark Ektar is giving you higher sensitivity due to better reciprocity. This assumes you are shooting them at box speed.

Ektar will provide the highest resolution, due to its finer grain combined with higher contrast.
But you also have to factor the quality the optics plus the ability to make long exposures in a stable manner. Still, you're dealing with a really tiny negative, so don't expect crisp large prints.